What You Should Know About Fastener Selection

Common Mistakes in Fastener Selection

Standard fasteners are divided into 10 categories. When choosing standard fasteners, it should be determined according to the use occasions and functions of the standard fasteners.

1. Coarse Teeth Instead of Fine Thread

There are many important connecting nuts and bolts on the machine, such as the driveshaft, and most of the bolts are fine thread. If the precision parts are missing during maintenance, some maintenance personnel will use coarse tooth bolts instead, which should be avoided. Because the fine-tooth bolt has a large inner diameter, small pitch and external Angle, high strength, good self-locking performance, and strong ability to bear impact, vibration, and exchange load. Once the coarse tooth bolt is used instead, it is easy to loosen or take off, disassemble, and even cause mechanical accidents.

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2. Pore Not Worthy

Nuts and bolts that are subjected to transverse load and shearing force on the machine, such as drive shaft nuts and bolts and flywheel nuts and bolts, shall be fitted with the nuts and bolts holes for transition fit, and shall be sturdy and reliable in assembly and able to withstand lateral force. Someone in the assembly process does not pay attention to check, nuts and bolts, and nuts and bolt holes still continue to install when there is a large gap, which is easy to happen bolt loosening or cutting accident.

3. Thickened Nuts Increase Connection Reliability

Some people mistakenly believe that thickening the nuts and bolts increases the number of loops of the thread and improves the reliability of the nuts and bolts joint. But in fact, the thicker the nuts and bolts, the more uneven the load distribution between the threads of each ring, and the easier it is to loosen the connection.

4. Multiple Washer for One Nut

After the installation is completed, sometimes the bolt is too long, so someone will install extra spring washers on the bolt. In this case, the spring washers will break unevenly during the hardening process, thus reducing the pre-tightening force of the bolt, and may produce an eccentric load, reducing the reliability of the nuts and bolts connection.

5. The Tighter the Better

Many staff members have such a misunderstanding: that is, the nuts and bolts should be ”rather tight than loose”, so they deliberately increase the tightening torque, resulting in bolt slip buckle. In addition, some of the important nuts and bolts need to be tightened with torsion, but some people because of the effort to tighten with a movable wrench, result in insufficient torque, resulting in loose bolts, and even lead to mechanical failure.

6. Too Big A-Gasket Won’t Hurt

Sometimes there is a lack of washers of appropriate size, and some workers will replace them with washers of larger inner diameter. In this case, the small contact area below the nuts and bolts-head and the washers will reduce the bearing pressure or locking force of the washers. If there is vibration and impact in the working environment, the nuts and bolts are easy to loosen.

7. Inappropriate Locking

Important nuts and bolts should be locked by an anti-loosening device after assembly is completed, which is illustrated in four cases. If the opening pin is used for locking, too thin opening lock or half opening lock shall not be used for locking. If the spring gasket is used for locking, the gasket opening is not allowed to be too small; If the lock piece is used to lock, the lock piece shall not be locked at the edges and corners of the nuts and bolts; If double nut locking is used, thinner nuts and bolts shall not be installed outside.

8. False Strong

If the nuts and bolts or threads are rusty, or scale, iron filings, and other impurities, must be cleaned before assembly; The joint surface of the connection has burr, sand and other impurities should also be removed. Otherwise, when tightening the nut bolt, it appears to be tightened on the surface, but in fact, the connection is not really tightened. Under such false firmness, nut bolts will loosen quickly if vibrations, load shocks, and temperature changes occur.

Selection Principle and Determination of Fasteners

Standard fasteners are divided into ten categories. When choosing standard fasteners, it should be determined according to the use occasions and functions of the standard fasteners.

①Bolt: bolts are usually matched with nuts (usually with one or two washers) and are used for connection and fastening.

②Nut: nuts and bolts are used together.

③Screw: the screw is usually used alone (sometimes with washers), and usually plays the role of tightening or setting.

④Stud bolt: studs are generally threaded at both ends (single-headed studs are single-ended with threads), usually ahead of rib firmly screwed into the body of the components, the other end, and nut match, play the role of connection and fastening, but to a large extent also has the role of distance.

⑤Washer: the washer is used between the supporting surface of bolts, screws, and nuts and the process supporting surface to prevent loosening and reduce the stress on the supporting surface.

⑥Self-tapping screw: the screw hole of the workpiece matched with the self-tapping screw does not need to be tapped in advance, and the internal thread is formed when the self-tapping screw is inserted.

⑦Rivet: the rivet has a head at one end and no thread at the rod. When in use, the rod is inserted into the hole of the connecting piece, and then the end of the rod is riveted and tightened to connect or fasten.

⑧Pin: the pin is set into a workpiece when in use, usually for connection or positioning.

⑨Check ring: The retaining ring is usually on the shaft or in the hole to limit the axial direction of the workpiece.

⑩Wood screw: Wood screws are used to screw into the wood for joining or fastening.

Nuts and Bolts Selection Principle

From the processing, assembly work efficiency consideration, in the same machinery or engineering, should minimize the use of standard parts of the variety.

Considering the economy, we should give priority to the selection of commodity standard parts of nuts and bolts.

According to the expected use requirements of standard parts, according to the type, mechanical properties, precision and screw thread, and other aspects to determine the selection of varieties.

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Common Types of Fasteners

Bolts

①Bolts have a hexagonal head, square head, refer to the national standard GB5780 – GB5790, etc.

②Bolts for reaming holes: when in use, the bolts should be tightly inlaid into the holes made of reaming to prevent the dislocation of the workpiece, refer to GB27, etc.

③Arrest bolt: there is a square neck, with vertebrae, refer to GB12-15, etc.

④Special purpose bolts: such as T-slot bolts, refer GB37; Looper bolt, see GB798; For anchor bolts, refer GB799, etc.

⑤Steel structure with high strength bolt connection pair: generally used in construction, bridge, tower, pipe support and lifting machinery and other steel structure friction connection occasions, refer GB3632, etc.

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Nuts

①Nuts for general use: mainly hexagon nuts, other square nuts, many varieties, refer to GB41, GB6170-6177, etc.

②Slotted nut: mainly refers to hex slotted nut, namely in the hex nut above the processing of bad. It is used with screw bolts with holes and split pins to prevent the relative rotation of bolts and nuts, refer to GB6178 — 6181, etc.

③Lock nut: refers to nuts with a locking function, including hexagonal locking nuts with nylon inserts, such as GB889, GB6182, GB6183, and all-metal hexagonal locking nuts, as GB6184 — 6187.

④Nuts for special use: such as disc nuts, refer GB62; Ring nut, see GB63; Cover nut, refer GB802, GB923; Knurled nuts, refer GB806, GB807 and insert nuts, refer GB809, etc.

Screws

①Machine screws: due to the head and groove types of different and divided into many varieties. The head type has a cylindrical head, pan head, countersunk head, and half countersunk head several kinds, the head shape is slotted (a word material), and the cross groove two kinds. Refer GB65, GB67-69 and GB818-820, etc.

②Set screw: the end of the set screw is used to prevent the mutual displacement between the workpiece and transfer less torque. Refer GB71, GB73-75, GB77, GB78, etc.

③Socket head cap crew: Hexagon socket screw is suitable for small installation spaces or where the screw head needs to be embedded. Refer GB70, GB6190, GB6191 and GB2672-2674, etc.

④Special purpose screws: such as setting screws, refer GB72, GB828, GB829; Non-release screws, refer GB827-839, GB948, GB948 and lifting ring screws, refer GB825 etc.

Stud bolts

①Double-headed studs of unequal length: suitable for one end of the screw into the body of the components, to connect or tighten the role of the occasion. Refer GB897-900, etc.

②Double end stud of equal length: suitable for connecting ends and nut matching, play the role of connecting or setting the distance. Refer GB901, GB953, etc.

Washer

①Flat washer: used to overcome the unevenness of the workpiece bearing surface and increase the stress area of the bearing surface. refer GB848, GB95-97 and GB5287.

②Spring (elastic) washers: spring washers see GB93, GB859, etc., elastic washers refer to GB860, GB955, etc.

③Stop washers: with inner tooth lock washers, see GB861; Outer tooth lock washer, see GB862; Single lug stop washer, see GB854; Double ears stop washers, see GB855; For round nut stop washers, refer to GB858, etc.

④Bevel washers: To accommodate the slope of the workpiece bearing surface, oblique washers can be used. For square inclined washers with I-steel, see GB852; For square inclined washers of channel steel, refer to GB853.

Self-tapping screw

①Common tapping screw: thread conforms to GB5280 (thread for tapping screw), large pitch, suitable for use on thin steel plate or copper, aluminum, and plastic. Refer GB845 — 847, GB5282 — 5284, etc.

②Tapping locking screw: the thread conforms to the common metric coarse thread, suitable for use in the need of vibration resistance. Refer GB6560-6564.

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Rivet

①Hot forged rivets: generally large size, used in locomotives, ships, boilers, etc., usually through hot forging to shape the head. Refer GB863-866.

②Cold heading rivets: generally diameter ≤16mm, usually by cold heading to make the head. Refer GB867 — 870, GB109, etc.

③Hollow and semi-hollow rivets: Hollow rivets, see GB976; Semi-hollow rivets, refer to GB873-875, etc.

④Special purpose rivets: there are headless rivets, refer GB1016; Tubular rivets, refer GB975; For label rivets, refer GB827, etc.

⑤Blind rivets: single riveted rivets, widely used in recent years, is a new type of rivets, rapid, safe, convenient, and have the advantages of being waterproof, and anti-leakage.

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Pin

①Cylindrical Pins: Cylindrical Pins with or without thread, see GB119; Cylindrical pin with internal thread, refer GB120; Cylindrical pin with external thread, refer GB878; Elastic cylindrical pin, refer GB879; Cylindrical pin with hole, refer GB880, etc.

②Taper pin: cylindrical pin with or without thread, refer GB117; Cylindrical pin with internal thread, see GB118; Screw taper pin, refer GB881; Open taper pin, refer GB877.

③Slotted pin: generally matched with screw bolts with holes and slotted nuts to prevent loosening of bolts and nuts. Refer GB91.

Check ring

①Resilient retaining ring: The elastic retaining ring with holes. refer GB893; Elastic retaining ring for the shaft. Refer GB894 and GB896 for shaft opening retaining ring.

②Steel wire retaining ring: steel wire retaining ring with holes, see GB895.1; Wire retaining ring for shaft, refer GB895.2 and wire locking ring, see GB921.

③Lock retaining ring for shaft parts: retaining ring with taper pin locking, refer GB883; ReferGB884, GB885, and so on for retaining rings with screw locking.

④Shaft end retainer ring: For shaft end retainer ring fastened with screws, refer to GB891, and for shaft end retainer ring fastened with bolts, refer to GB892.

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Wood screw

It is divided into many varieties because of the head shape and groove shape. Head type has a round head, countersunk head, half sunk head several kinds of head groove for slot (a word slot), and cross slot two. Refer GB99-101, GB950-952, etc.

Self-tapping screws and self-tapping locking screws

Ordinary tapping screws are not classified according to mechanical properties. As long as the appropriate specifications are selected, refer to 3.6 and Table 3 in GB3098.5), they can meet the general use requirements.

The mechanical properties of self-tapping locking screws are divided into two grades: A and B. Grade A is high strength grade; Class B is a low strength grade.

Self-tapping screws and self-tapping locking screws

Ordinary tapping screws are not classified according to mechanical properties. As long as the appropriate specifications are selected, refer to 3.6 and Table 3 in GB3098.5), they can meet the general use requirements.

The mechanical properties of self-tapping locking screws are divided into two grades: A and B. Grade A is high strength grade; Class B is a low strength grade.

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Confirm Specification

①The first series of values should be chosen as far as possible for the diameter specification. The values in parentheses in the product standard-size table and the values in the specification table should be avoided as far as possible.

②Length specifications generally do not adopt specifications other than those specified in the product standard. General bolt or nut matching connection, the thread end exposed (0.2-0.3) D length is appropriate.

YIJIN Hardware specializes in five-axis machining and other high-precision parts machining, especially as the top fasteners manufacturer in China, YIJIN Hardware provide all kinds of fasteners, such as spring washer, eye bolt, blind rivet, coach bolts, hex screw, hex nut, cap screw, nuts and bolts, nut bolt, washer screw, concrete screws, tapcon screws, stainless steel screws, split pin, anchor fastener, decking screws, wing nut, tek screws, wood screws, rivets, tapping screw, rivet nut, and coach screws, which are widely used in all kinds of high-tech and precision industries, such as robot parts, UAV parts, medical equipment parts, aviation parts, automation equipment parts, aerospace, ship parts, connector parts, military parts and so on.

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