Threaded Fasteners – All You Need To Know

What Are Threaded Fasteners?

Threaded fasteners are mechanical parts with internal or external threads. They are generally used as fasteners to facilitate the combination of multiple components. The most common threaded fasteners are screws, nuts, and bolts. However, there are other threaded fasteners, such as cage nuts, threaded inserts, threaded rods, etc.

A threaded fastener connection is a widely used detachable fixed connection, which has the advantages of simple structure, reliable connection, and convenient assembly and disassembly. The traditional thread detection method is to use a thread gauge for contact or use a universal tool microscope for manual measurement. The workload is large, the working efficiency is low, and the measurement results are easily affected by the operator.

threaded fasteners manufactured by YIJIN Hardware

According to the shape of plane graphs, threads can be divided into a triangle, rectangle, trapezoid, and serrated threads. According to the winding direction of the helix, threads can be divided into left-hand thread and right-hand thread. It is stipulated that when the thread is upright, the helix rises to the right into a right-hand thread, and rises to the left into a left-hand thread.

Characteristics of Threaded Connection

①Great shaft force can be generated when threads are tightened;

②Threaded connection can easily realize self-locking;

③Small size;

④It is simple to manufacture and can maintain high precision.

Threaded Fasteners Type Selectivity

Bolted Connection

Used to connect two thinner parts. The connecting piece is provided with a through-hole. There is a seam between the rod and hole of the ordinary bolts, the processing requirement of the through-hole is relatively low, with a simple structure, easy to disassemble, and widely used.

Studded Connection

It is used where one of the connected parts is thick and not suitable for bolt connection, and the thicker connected parts have poor strength and need to be disassembled frequently. Threaded holes are processed on thick parts and smooth holes are processed on thin parts. Bolts are screwed into threaded holes, and a nut is used to tighten the thin part.

Screw Connection

Bolts(or screws) are screwed directly into the threaded hole of the connected parts without nuts. Its structure is simpler and more compact than the stud. A screw connection is used for the thicker one between the two connected pieces and does not need to disassemble often, so as to damage the threaded hole.

Set Screw Connection

Screw into the threaded hole of the end of the thread against the surface of another part or into the pit of another part, in order to fix the relative position of the two parts. The structure of the set screw connection is simple, that some can change the part’s circular or shaft directions position randomly, so as to adjust, such as the fix of the electrical device rotary switch.

Fastening Principle of Threaded Fasteners

A thread can be defined as an inclined surface around a cylinder and is equivalent to an inclined surface. Conversely, the unfolding of a thread is an inclined surface. The self-locking phenomenon refers to that if the action line of the net force Q acting on the main force of the object is within the friction Angle, no matter how big the force is, there will always be an all-reaction force R in balance with it, and the object will remain static.

Conversely, if the action line of the resultant force Q is outside the friction Angle, no matter how small the force is, the object cannot keep balance. This kind of equilibrium condition which is independent of force but related to friction Angle is called the self-locking condition. The object under this situation still keeps equilibrium, which is called the self-locking phenomenon. The resultant force R of the friction angle and the normal reaction force N of the self-locking phenomenon and the friction force F are called the total reaction force of the support facing the object. That is when the friction force F up to its F maximum value, at the same time, the included Angle an also reaches its maximum value b which is called the Angle of friction.

Sunk Screw

Used for the situation where the thread diameter is less than 10mm and the strength requirement is not high. The head of the screw or part of it sinks into the connected part. This structure is mostly used on occasions that require a flat outer surface, such as an instrument panel.

Self Tapping Screw

It’s applicable to situations where connection strength is not required. But generally, the bottom hole should be made in advance. If self-drilling and tapping screws with drill bits are used, there is no need to prefabricate bottom holes for non-ferrous metals, wood, etc.

Wood Screw Connection

Usually applied in the wood structure connection. Depending on the hardness of the material and the length of the wood screw, wooden parts may not be prefabricated or prefabricated with a certain size and depth.

Threaded Fasteners Component Parts Connection

Washers and fasteners with external thread are manufactured and supplied in complete sets by a standard workshop professional factory. These kinds of connected parts are convenient to use, time-saving, safe, and reliable, and are usually used in connected situations where fasteners are closely connected.

Thread Forming Screws Connection

The thread is arc triangular interface, the screw surface hardened, can be screwed into the metal material of the prefabricated hole, extrusion to form an internal thread. The internal thread formed by extrusion is more than 30% stronger than that by cutting. The small tensile strength of the screw is 800MPa. Thread forming screw with low tightening torque and high locking performance, which is widely applicable to household appliances, the electrical industry, and the automobile industry.

Threaded Fasteners Marking

General Purpose Screw Threads

1) Coarse thread pitch of the common thread is not marked, fine thread pitch must be injected. If M20 is a coarse tooth, pitch 2.5mm is not marked; if M20×2 is a fine-tooth, pitch 2mm should be marked.

2) Note LH for the Left-hand thread, not for the right-hand thread.

3) Tolerance zone codes for thread include middle diameter and top diameter tolerance zones, lowercase letters for outer thread tolerance zones, and uppercase letters for inner thread tolerance zones. For example, m20-5G6G indicates that the middle diameter tolerance zone of the external thread is code 5g, and the top diameter tolerance zone is code 6G. If the middle diameter and the top diameter tolerance zone code are the same, such as M20-7H means that the inner thread middle diameter and top diameter tolerance zone are 7H.

4) The screw length of ordinary thread is specified as short (S), medium (N), and long (L), and the medium screw length (N) need not be marked, such as M24-5G6G-L, M20×1.5-6H-S-LH, or M20×1-6g. If the spinning length is a specific value, it can be directly marked, for example, M20-5G6G-40 indicates that the spinning length is 40mm.

Acme Thread Form

Labeled with common threads, such as Tr40×7LH-7H-L represents trapezoidal threads, nominal diameter of 40mm, pitch of 7mm, left rotation, tolerance zone code for 7H, long screw length.

55° Unsealed Pipe Thread

55° unsealed pipe threads, whose outer threads have two tolerance classes A and B, shall be marked out; Internal threads have only one tolerance class and do not need to be noted. For example, G1/4A refers to the non-threaded sealing pipe thread, which is the external thread, the size code is 1/4, and the tolerance grade is A; G1/4 means non-threaded sealed pipe thread, is an internal thread, dimension code 1/4.

Common Threaded Fasteners

Detachable connections can be made with bolts, screws, and nuts.

Bolts and Screws

Head bolts and screw heads come in a variety of shapes and can be used as clamp bolts, pair bolts, or mating bolts.

Bolts and Screws manufactured by YIJIN Hardware

Clamp Bolt

Used for fixing cover plate, flange plate, press plate, and other machine parts. Screw in-depth as a double-headed stud. Cylindrical bolts with inner hexagons can be countersunk, but can still be tightened like hexagon bolts.

Clamp Bolts manufactured by YIJIN Hardware

Butt Bolt

To be secured with nuts and washers. Pay attention to the flat contact surface of the bolt head and nut and washer.

Fitted Bolt

Used for fixing the position of machine parts or bearing transverse forces. This connection requires mating (H7/ K6), so it is more expensive. It is more economical to combine one or two matching pins with pair bolts.

Fitted Bolts manufactured by YIJIN Hardware

Slotted Head Cap Screws

The screw heads of slotted screws come in various shapes. This kind of screw can only be tightened with a screwdriver. The screw head of the Phillips screw has no slot through it, so the strength will not be weakened. Phillips screw is characterized by high strength, can be screwed more tightly, and the shape is good-looking.

Slotted Head Cap Screws manufactured by YIJIN Hardware

Tapping Screw

Used for fixing company signboard and guard board on an iron plate.

Tapping Screw manufactured by YIJIN Hardware

Stud

The stud is composed of the screw into the end (chamfered), screw, and nut end (top). The purpose is the same as clamping studs. The advantage is that the clamping stud will damage the thread after repeated loosening, while the screw end of the stud can always be screwed in. Remove the studs by removing the nuts. Screw in depth should conform to the strength of the screw material, so as not to break the screw.

Stud manufactured by YIJIN Hardware

Set Screw

The screw is threaded on the whole length, and there is a groove at the end for screwing and tightening, which is used to fix the positioning ring, shaft sleeve, and other machine parts to prevent movement or torsion dislocation. A stud is a variant of a screw used to secure removable parts.

Set Screw manufactured by YIJIN Hardware

Nut Type

The figure below shows several standard nut shapes. The length of the nut thread is important for the strength of the nut screw connection. Thread length determines the number of thread bearings. For most nuts, the nut height is equal to the thread length. The exception is blind nuts. Height of standard nut =0.8 x nominal diameter of the thread. Height of flat nut ﹤ 0.5× d, only used for small force or loose place. If the force is large, super high nuts must be used, and the height is >1+d.

Nuts manufactured by YIJIN Hardware

Threaded Fasteners Test Methods and Characteristics

Thread is a fastening connection structure widely used in the industrial field. In military models and products, more than 80% of the structural connection is completed by a thread. Whether the thread is qualified or not directly affects the assembly performance and use of the safety of the equipment.

Thread is a complex three-dimensional surface, it is composed of many geometric parameters, such as tooth height (large diameter, medium diameter, small path), tooth side Angle, pitch, taper, roundness, straightness, and tooth bottom arc radius. Theoretically, the quality level of screw thread can be determined accurately only when each parameter of screw thread is tested separately, which is also the development direction of screw thread testing technology.

As early as the early 1980s, some developed industrial countries developed a thread indicator gauge to replace the traditional thread through, stop gauge. The indicator gauge can quantitatively detect the specific value of the parameter, and it can also separate many individual parameters of the thread from the comprehensive measurement, and give the detection value of the individual parameter so that the quality of the thread can be better controlled.

Up to now, some advanced industrial countries have as many as dozens of thread detection means. In order to standardize the uniform thread inspection and testing methods, the United States first issued in 1979 ANSI/ASMEB1.3-1979 (confirmed in 2001) “Thread size Acceptance Inspection Method” standard, better to solve the unified problem. This standard stipulates three methods of measuring thread, namely the “21” method, “22” method, and “23” method, the specific content is shown in Table 1.

Common Inspection Methods

In the measurement of the threaded parameters, according to the different measurement equipment, the main threaded parameters measurement can be divided as follows:

Thread Pass and Stop Gauge Detection

According to Taylor’s principle, the traditional stop-gauge test method can only meet the minimum requirements of thread testing. The advantages of this inspection are fast, economical, and practical. For the enterprise with a higher production technology level, such as YIJIN Hardware, the quality level of thread can be better controlled by using a qualified thread forming cutter and special thread processing equipment (such as thread tap, die, rolling machine, rubbing machine, etc.).

Thread Pass and Stop Gauge Detection

The main disadvantage of this inspection method is that it can only qualitatively check whether the pitch diameter of the thread is qualified, and can only know whether the middle diameter of screw thread is located between the smallest single middle diameter and the largest acting middle diameter, and it is possible to know the specific value of screw size. Half Angle error, pitch error, and all kinds of shape error parameters can not be controlled quantitatively.

However, with the development of industry, especially the aviation, and aerospace industry, the interchangeability, and reliability of screw thread connections are increasingly required, and the traditional comprehensive measurement method is difficult to meet the testing needs.

Thread Micrometer

Screw micrometer belongs to special screw micrometer, the structure is shown in Figure 2, screw micrometer has a special measuring head, the shape of the measuring head is made to match the shape of the thread tooth, that is, one is v-shaped measuring head, match the convex part of the tooth shape, the other is conical measuring head, match the tooth shape groove. The micrometer has a set of interchangeable measuring heads, each pair of which can only be used to measure threads in a certain range of pitch.

Thread Micrometer

According to the technical indicator of thread micrometer, the maximum comprehensive error is ±0.028mm, because there is a certain Angle error of the probe, the pitch of the workpiece external thread and the tooth side Angle also has a large error, so when using the absolute method to measure, the uncertainty of diameter measurement can reach 0.10mm. This method is used to measure the middle diameter of the external thread of the workpiece with a low precision requirement.

Three-Pin Test

Three pins (Figure 3) are a set of three measuring pins of the same diameter, which are used to measure the middle diameter of the thread indirectly.

Three-Pin Test

Three measuring pins were put into the tooth groove on both sides of the thread, and the whole outer diameter was measured with a lever micrometer. The single middle diameter of the thread was calculated by the function of the middle diameter of the thread and measuring pin diameter, tooth Angle, and pitch. In order to simplify the calculation process, a measuring pin of an appropriate diameter should be selected.

When this method is used for measurement, inspectors are required to have certain detection experience and the technique is highly detailed, so the measurement stability is greatly affected by the operation, and it is not recommended for general inspectors to operate it.

The formula for calculating the diameter of thread d2 is:

The formula for calculating the diameter of thread d2

In the formula, the value measured by m-micrometer, mm;

d0-pin’s diameter, mm;

α/2-half of thread angle, (°);

P-workpiece pitch, mm.

Gauge Type Integrated Thread Measuring Instrument

Gauge Type Integrated Thread Measuring Instrument

At present, some foreign enterprises have successfully developed high-precision gauge thread integrated measuring instruments (see Figure 4) on the basis of key technological breakthroughs. The most typical representative is the United States zhang sen thread professional manufacturing company developed thread comprehensive measurement instrument, which can detect the various parameters of the thread, with high precision measurement, and is easy to operate.

The high-precision thread comprehensive measuring instrument adopts the contact thread measurement method (principle as shown in Figure 5). Compared with the traditional measurement method and non-contact measurement method, it has great advantages and feasibility. It has the advantages of high accuracy, easy to use and strong function, etc., and has great reference value for the measurement of thread.

Image Method

So far, projector and universal tool microscope (Figure. 6) are commonly used for thread measurement by image method. The projector measures the parameters of the studs by means of visual positioning and coordinate translation through the enlarged contour of the measured parts. Due to the use of visual boundary alignment and the limitations of the projection method in measuring the thread diameter, the accuracy of the projection method is generally very rough.

A universal tool microscope uses an optical system to project thread contour into the eyepiece field of view and uses a grating ruler to translate, which can be used to examine various thread parameters. Especially, lens deflection can effectively solve the problem of screw Angle and has high measuring accuracy for the thread.

When using this method for measurement, it is necessary to locate the measurement reference line (usually the axis of the tight drawing piece), deflect, align and double, etc., which is not high detection efficiency and not suitable for the detection requirements of large quantities. It is restricted by the field of view of universal tool microscopes, which hinders the inspection work to some extent.

In order to reduce a lot of measurement errors caused by human observation, a device was developed to extract 2d contour data of screw thread by computer and automatically calculate various parameters of screw thread including middle diameter. For example, a thread contour measuring instrument (Figure. 7) uses a universal tool microscope and CCD to collect thread contour data and calculates thread parameters by the automatic measurement method of machine vision.

Image Method

FIG 6. universal tool-measuring microscope   FIG7. Thread contour measuring instrument

Laser Triangulation

Laser triangulation, as another nondestructive testing method, has received extensive attention. According to the triangulation principle of traditional optics (as shown in Figure 8), the data point set of the shaft section contour of the thread surface is obtained, and then the parameters of the thread are calculated.

Laser Triangulation

CCD received the laser beam, the data will be collected and analyzed, so as to simulate and fit the thread, but also by measuring the improvement of the head spectrophotometer so as to achieve the measurement of the thread section amount, according to the scan measured data, can quickly get the internal thread parameters.

This measurement method has the characteristics of non-contact, high precision, easy control, and so on, and can also be applied to small size high-speed measurements. However, this method is affected by the ambient temperature and the surface characteristics of the measured object, and the influencing factors should be taken into account in the later data image processing.

Coordinate Measuring Machine (CMM) Measurement

CMM is widely used in measuring boxes, frames, gear, cam, worm wheels, worm, blade, curve, curve surface, and so on in machinery, automobile, aviation, military industry, mold, and other industries. There are many methods to measure screw parameters through the transformation of CMM.

However, CMM is a kind of widely used universal equipment, which lacks a probe for thread measurement. It is necessary to customize the probe head for small size thread. The software development is also limited by the software platform of CMM itself, so it is difficult to customize the contour following the control system for the screw geometry. And its cost is much higher than the special thread measuring equipment.

Stylus Scanning Thread Contour Measuring Instrument

The stylus scanning thread contour measuring instrument (as shown in Figure 9) continuously scans and measures the upper and lower contour surfaces of the axial section of the thread, and then calculates the parameters of the thread, such as middle diameter, large diameter, small diameter, pitch, tooth profile half Angle and taper, according to the obtained contour information.

Stylus Scanning Thread Contour Measuring Instrument

The screw thread measuring fixture ensures the accuracy of the reference axis of the screw thread and provides a guarantee for the high-precision measurement of parameters such as tooth Angle and pitch. At the same time, the thread parameters can be calculated and marked on the thread contour graph, which greatly improves the measurement efficiency.

Measurement data can also be saved or output in text form. Manufacturers can make corresponding adjustments to processing machines or tools based on this information, and metrology workers can perform detailed identification and evaluation of measurement results. This kind of high precision, high efficiency, and high information detection method is of great significance to product quality inspection and quality management of production enterprises.

Three Basic Types of Anti-Loosening Methods for Threaded Fastener Connections

Non-Detachable Anti-loose

This is a kind of anti-loosening method which changes the detachable thread connection into the non-detachable thread connection by means of welding, bonding, or punching point riveting. It is a very reliable traditional anti-loosening method. The disadvantage is that threaded fasteners cannot be reused. And the operation is troublesome. It is often used on some important occasions which require high reliability and no disassembly.

Anti-Loosening of Mechanical Fasteners

The use of mechanical fasteners to make threaded parts and connected parts or between threaded parts and threaded parts fixed and pin tight, to prevent loosening. The advantage of this method is that it is reliable in preventing loosening, which generally depends on the static strength or fatigue strength of the mechanical fixture (or the fastener itself, such as the slotted nut).

Its disadvantage is to increase the weight of fastening connection, manufacturing and installation trouble, can not be mobile installation, so the cost is higher. Because of its high reliability, it is still widely used in some important parts of mechanical products and aerospace products.

Increase the Resistance to Friction

The purpose of anti-loosening can be achieved by increasing the friction force between threads or bolt (screw) head and end face of the nut or increasing the friction force of both at the same time.

This anti-loose method is less reliable than the above-mentioned type a or type b methods, but its biggest advantage is that it is not restricted by the use of space, can be repeatedly assembled and disassembled many times, and can be assembled by mobile, and some of them Fasteners (such as nylon ring lock nuts, all-metal lock nuts), its anti-loosening reliability has reached a very high level. Therefore, this anti-loosening method is mostly used in the mechanical manufacturing department and aerospace field.

Commonly Used Anti-Loose Methods of Threaded Fasteners

Non-Detachable Loose Bolt (or Screw) Head and Nut End Face Point Riveting

Non-Detachable Loose Bolt (or Screw) Head and Nut End Face Point Riveting

After tightening, the bolt (or screw) nut is deformed locally by means of impact point riveting to prevent them from loosening each other. Reliable anti-loosening can be used for any connection without disassembly.

Bonding of Locking Adhesives

Bonding of Locking Adhesives

In the matching thread surface coated with epoxy resin or anaerobic adhesive, adhesive curing can be firmly bonded to the matching thread, to achieve the purpose of locking loose. Different adhesives often have different locking abilities. Fasteners coated with epoxy resin have high bonding strength and are not removable. Although fasteners coated with anaerobic adhesive can be disassembled, it is difficult to clean the residual adhesive on the surface of the thread after disassembly, and the thread may be damaged, so the fastener should not be used again.

Adhesives can also be used as a seal for threads, but they cannot withstand high temperatures. The best adhesives work at 230 ° C; The worst adhesives work at only 94℃. Reliable anti-loosening can be used for any connection that does not need to be removed.

Anti-Loosening of Mechanical Fixing Parts

Slotted Nut with Split Pin

Anti-Loosening of Mechanical Fixing Parts Slotted Nut with Split Pin

The cotter pin passes through the slot of the nut and the pinhole at the end of the bolt to lock the nut and bolt directly. It can be used for important movable parts, such as the connection of joystick movable joints in the cockpit of aircraft and vehicles, in the loose connection state without tightening (i.e. without applying pre-tightening force). It can also be used in particularly important parts that require high reliability under long-time harsh vibration conditions. In this case, nuts and bolts must be tightened with proper pre-tightening force, otherwise, in an untightened loose connection, the cotter pin or nut will cause fatigue failure, resulting in loosening failure of the fastener. Such accidents are common in many connections subjected to harsh working conditions.

Lock Washer

Use single or double steel washers to fix the nut and the connected part together or fix two nuts to each other.

Reliable anti-loose can be used for high-temperature parts of the anti-loose connection. Often used in important parts of engine products.

Locking Steel Wire

Locking Steel Wire

With steel wire into the screw head or nut hole, so that several screws or nuts are together and locked. Although it is difficult to assemble, it is still used in important situations, especially in important parts of aerospace products, because it is reliable and loose. Can be used to prevent loose connection of bolts or screws.

Increase the Friction and Prevent Loosening

Toothed Face Locking Nuts and Locking Screws of Free Rotation Type

Increase the Friction and Prevent Loosening Toothed Face Locking Nuts and Locking Screws of Free Rotation Type

Support surfaces under nut and screw heads are knurled or serrated. When the nut or screw is tightened, friction resistance occurs between the supporting surface and the connecting piece, especially when the “sawtooth” is embedded on the surface of the connecting piece, the locking is very firm. The tooth shape of the support surface and the clamping force during tightening have a significant influence on the locking performance. Stable torsion – tension and high enough clamping force are the prerequisites for maintaining the locking capacity of this fastener. The test proves that they have good anti-loosening performance.

Should not be used with a washer or in threaded connections that cannot withstand high clamping forces or where the connected surfaces are sensitive to scratches and corrosion. In the use of this anti-loosening method, attention should be paid to the reasonable matching of hardness. In general, the hardness of the clamped parts should be lower than that of fasteners.

Double Nut

Double Nut

The traditional assembly method of double nuts is to tighten the inner nut first, then tighten the outer nut, and then reverse the inner nut, so that the threads between the two nut heights produce small elastic deformation to obtain additional friction and prevent loosening. The practice has proved that this assembly method is not reliable to prevent the loosening of double nuts. The disadvantage is that when the nut is turned inside, the fastening system is unloaded, the clamping force becomes smaller and the anti-loose ability decreases. The new assembly method cancels the procedure of “reverse screw the inner nut”, that is, screw the inner nut first, then screw the outer nut, and apply the same tightening torque to the two nuts, so that the clamping force of the fastening system can be maintained at a higher level. The test at home and abroad proves that the anti-loosening ability of the double nuts is greatly improved by adopting the new assembly method. It is one of the anti-loosening methods with higher anti-vibration life among all kinds of threaded fasteners.

With double nuts against loose, although increased the weight, the structure is simple, anti loose effect is good, can be used for high temperature, so in some important situations are still used, such as the engine thread connection against loose.

All Metal Lock Nuts of Effective Torque Type

At the upper end of the nut body for non-circular closing or slotted closing (the latter is also known as slot beam-type lock nut), the thread is partially deformed. After the bolt is screwed into the nut, the closing part of the nut expands outward, using the flexibility of the closing part, so that the thread pair is horizontally pressed, eliminating the gap between threads, increasing the friction force of threads, so that the bolt and nut firmly locked together.

The anti-loosening effect is good, and the anti-loosening performance of the slotted beam-type lock nut is better. When used with bolts with higher screw precision, the anti-loosening performance can be improved; When the bolts with higher hardness corresponding to the nut hardness are used, the service life of repeated assembly and disassembly can be significantly improved. Of all-metal lock nuts, slotted beam-type lock nuts have the best reusability.

Can be used for any fastening part except the movable part.

Locking Nuts with Non-Metallic Insert, Effective Torque Type

Insert a nylon ring on the upper end of the nut, the inner diameter of the nylon ring is slightly smaller than the middle diameter of the thread. When the bolt is screwed in, the nylon ring is extruded out of the inner thread, and the extremely elastic nylon material forms a large and very stable friction resistance with the bolt, achieving a reliable locking.

Good anti-loose performance, can be repeatedly assembled and disassembled for use, suitable for the use of harsh impact, and vibration. Can be used with any bolt from low precision to high precision; Can also be used with any bolt from low strength to high strength. Its temperature is limited by nylon ring material, generally -50 ~ +100℃.

Spring Washer

Use spring tension to provide locking action for threaded connections. Its advantage is simple structure, low cost, and ease to use. It is widely used to prevent the loosening of unimportant parts of general mechanical and electrical equipment.

The main disadvantages of spring washer

The poor anti-loosening effect is not suitable for the use of strong impact, vibration parts; Electric galvanized or cadmium steel washers often produce delayed hydrogen embrittle fracture, resulting in hidden dangers and subsequent failure accidents. The sharp edge of the washer opening is easy to damage the connected surface.

The fastening system is subjected to deflection, the centrality of bolt force is destroyed, the bolt bears additional bending stress, and the fatigue performance of the threaded connection is reduced.

This adverse effect is particularly significant under severe external load. Increasing the flexibility of the connector, that is, reducing the stiffness of the connector, may lead to a decrease in the fatigue performance of the threaded connection. Due to the open ring structure, under the action of clamping force, there may be a failure due to the increase of inner diameter. Therefore, spring washers are not used in important applications.

Elastic Washer

Use spring tension to provide a locking effect for threaded connections.

The poor anti-loose effect is mostly used in unimportant connection parts of electromechanical equipment.

Electrically galvanized or cadmium steel washers can produce hysteretic hydrogen embrittlement fracture, resulting in hidden hazards and subsequent failures.

Toothed Lock Washer

When the nut or screw is tightened, the warping teeth of the washer are flattened, increasing the friction resistance between the thread and the support surface and providing a locking effect for the thread connection.

Because the warped teeth are embedded in the surface of the screw head (or nut) and the connected part, the damage caused by it will increase the sensitivity to corrosion, and for fasteners or connected parts under high stress, this damage may lead to the generation of cracks. The warping teeth of the washer may crack or break under high clamping force. The inner and outer serrated lock washers have greater bearing capacity than the inner and outer tooth lock washers.

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