A Complete Guide to Bolts

How Are Bolts Made?

Bolt processing methods are generally divided into three kinds: cold/hot forging screw head processing; Direct head forming machining without cold or hot forging; impact molding. Machining high-strength bolts generally use cold hot forging to form a head shape.

hex bolts manufactured by YIJIN Hardware

The specific manufacturing process of the bolt is as follows:

  1. Green rod
  2. Cold drawing
  3. Spheroidizing Annealing(Preheat treatment)
  4. Phosphorus removal
  5. Pickling
  6. Cold drawing
  7. Cold forging forming
  8. Thread processing
  9. Feeding
  10. Phosphorus removal
  11. Quenching
  12. Cleaning
  13. High tempering
  14. Water cooling
  15. Drying
  16. Fuel injection
  17. Surface finish
  18. Quality inspection

Types of Bolt

Hexagon-headed bolt(full thread): Grade A grade B DIN EN ISO 4017-2001.

Full thread hexagon head bolt: Grade A grade B DIN 933 – 1987.

hex bolts supplied by YIJIN Hardware

These three criteria can be applied to the bolt picture below. DIN933 is the German standard bolt, is also a hexagon head bolt (full tooth) mechanical bolt, and is also used for nuts with cylindrical threaded fasteners. 

Hexagon-headed bolt: Product grades B DIN 931-2 – 2009.

inner hex bolts manufactured by YIJIN Hardware

These three criteria can be applied to the following bolt picture. DIN931 is the German standard bolt, hexagon head bolt (half tooth), for the purpose of connection without full thread, this standard bolt screw body is only two-thirds of the thread.

DIN912 is the German standard bolt, known as hexagon socket head screw, the following two pictures are applicable to the DIN912 standard, one is the bolt head without fancy teeth, and the other is the bolt head with teeth pattern (also known as anti-skid teeth).

Hexagon flange bolts: Product grade B DIN 5787 – 1986.

DIN5787 is a kind of bolt of German standard, called hexagon flange face bolt. The following picture applies to the DIN5787 standard. The most important role of hexagonal flange bolts is that hexagonal is more than a flange surface, which can reduce the hexagonal stress area and increase the contact area of bolts during connection.

hex cap bolt manufactured by YIJIN Hardware

So that it is not easy to break, and reduce the use of gaskets, thus saving the cost and saving the bolt installation connection time!

The above four bolts are the standard number of bolt-standard parts. For more information about standard bolts and non-standard bolts, please contact Yijin Hardware. Yijin hardware is committed to the production of bolts for more than 20 years and has a rich production of bolt manufacturing ability.

Materials of Bolt

Different materials are used according to the strength level of the bolt:

At present, the main standard parts on the market are carbon steel, stainless steel, copper, titanium alloy, and super duplex steel.

carbon steel bolts supplied by YIJIN Hardware

  1. Low carbon steel C%≤0.25%, China known as A3 steel, the world is basically known as 1008,1015,1018,1022 and so on, mainly used for grade 4.8 bolts, and grade 4 nuts, small screws, and other bolts without hardness requirements. (Note: Drilling tail screws are mainly adopted 1022 material).
  2. Medium carbon steel 0.25%<C%≤0.45%, China known as no. 35 steel, no.45 steel, the world is basically known as 1035, CH38F, 1039,40ACR, and so on. 
  3. High carbon steel C%>0.45%, so far there is basically no material on the market.

Bolts Thread Processing Technology

The main processing method of the external thread is rolling thread, threading and die tapping thread, etc., and the main processing methods of internal thread are taped thread (cutting tap, squeeze tap), car thread, etc.

The choice of thread machining method depends on the shape, size, batch size, and machining size of the product. Fastener bolts, screws, studs, and other external thread processing, due to large batch, most will use rolling thread for processing. Rolling thread is a scrap-free processing method. It is also a cold extrusion process for rolling screw blank materials at indoor temperatures.

stainless steel bolts supplied by YIJIN Hardware

The process is essentially a process of material metal redistribution. The rolling thread has a smooth surface and continuous metal fiber flow, and the static tensile strength is increased by 20%~30% compared with the cutting thread.

General high-strength bolts need to be tempered, if the thread is processed first and then tempered, proper measures should be taken in the heat treatment process to avoid thread deformation and surface treatment decarbonization after heating.

In the case of higher requirements for fatigue mild, it is necessary to adjust and quench the thread before rolling the thread, which can not only avoid the decarburization of the root thread but also make the residual compressive stress at the bottom of the tooth.

Carriage Bolts manufactured by YIJIN Hardware

For example, the high strength double end stud’s fatigue strength can be increased by 200%, but the service life of the roller is reduced and the manufacturing cost is increased.

Tapping thread is generally selected for large-scale processing of internal thread, which is economical and effective. The equipment used is a vertical single-axis threading machine, a horizontal double-axis automatic threading machine, horizontal four-axis automatic threading machine.

There are many types of bolts, up to 500,000 kinds, YIJIN Hardware as the famous custom fastener supplier with 20 years of fastener manufacture experience, provides customers with a wide range of custom fasteners, including screws, rivets, nuts and bolts, bolts, self-tapping screws, anchor bolt, toggle bolts, drywall screws, nut bolt, u bolt, concrete screws, eye bolt, wood screws, lag bolts, carriage bolt, wing nut, grub screw, lock nut, clevis pin, spring washer, decking screws, set screw, pan head screw, brad nails, stud bolt, dowel pin, pop rivet, split pin, tek screws, special rivet, expansion bolt, hex bolt, pocket hole screws, coach bolts, threaded inserts, contact us we can custom the fasteners you need.


Combined with all the above, we have learned the relevant knowledge background of fasteners. Fasteners play a pivotal role in the industrial era, and many industrial household products need bolts to connect and fix.

Yijin Hardware has more than 20 years of experience in the production of bolts, bolts of various sizes have produced more than 100 million pieces, and accumulated rich experience in the production of nuts and bolts, as well as fastener solutions.

Please contact Yijin Hardware fastener experts for custom u bolt solutions, we will design the fasteners and bolts you want for free and quickly, and tell you the use and choice of bolts, for your product fastening and connection custom-made.

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