Overview: Fastener, Nuts and Bolts, Types of Screws and Bolts

Table of Contents

Overview: Fastener, Nuts and Bolts, Types of Screws and Bolts

What is Fastener

What is Fastener

The general term for a type of mechanical parts used when two or more parts (or components) are fastener, also called standard parts. It usually includes the following 12 types of parts:

  • 1. Bolt
  • 2. Stud
  • 3. Screw
  • 4. Nut
  • 5. Self-tapping screws
  • 6. Wood screws
  • 7. Washer
  • 8. Retaining ring
  • 9. Pin
  • 10. Rivet
  • 11. Assembly and connection pair
  • 12. Welding nails

Bolt Fastener

Mechanical parts, cylindrical threaded fasteners with nuts. A type of fastener consisting of a head and a screw (cylinder with external threads), which need to be matched with a nut to fasten and connect two parts with through holes. This type of connection is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.


There is no head, only a type of fastener with external threads on both ends. When connecting, one end of it must be screwed into the part with internal threaded hole, and the other end must pass through the part with through hole, and then screw the nut to make the two parts tightly connected into a whole.

tap end studs bolts

Studs generally refer to double-ended studs, which are cylindrical fasteners with threads on both ends. It is widely used in electric power, chemical industry, oil refining, valves, railways, bridges, steel structures, automobile and motorcycle accessories, machinery, boiler steel structures, crane towers, large-span steel structures and large buildings.

Screws are a type of fasteners composed of two parts: a head and a screw. According to their use, they can be divided into three categories: machine screws, set screws, and special purpose screws. The machine screw is mainly used for the fastening connection between a part with an internal threaded hole and a part with a through hole, and no nut is required. (This type of connection is a screw connection, which is also a detachable connection. Matched with a nut for the fastening connection between two parts with through holes). Set screws are mainly used to fix the relative position between two parts. Special purpose screws have eyebolts for hoisting parts.

screw heads

Classified by screw structure:

1) Slotted ordinary screws

It is mostly used for the connection of smaller parts. It has pan head screws, cylindrical head screws, half countersunk head screws and countersunk head screws. Pan head screws and cylinder head screws have high nail head strength and are connected to common parts; the head of the half countersunk head screw is arc-shaped, and its top is slightly exposed after installation, and it is beautiful and smooth. It is generally used for instruments or On precision machinery; countersunk screws are used where the nail heads are not allowed to be exposed.

2) Hexagon socket and hexagon socket screw

The head of this type of screw can be embedded in the component, can apply a larger torque, and the connection strength is higher, and it can replace the hexagonal bolt. It is often used in joints with compact structure and smooth appearance.

3) Cross recessed ordinary screws

It has similar functions to ordinary slotted screws, and can be replaced with each other, but the cross-slotted ordinary screws have higher groove strength, are not easy to be bald, and have a more beautiful appearance. When in use, a cross-shaped screwdriver must be used for loading and unloading.

4) Eye screw

The eyebolt is a kind of hardware accessory for load-bearing during installation and transportation. When in use, the screw must be screwed to the position where the supporting surface fits tightly. It is not allowed to use tools to tighten it, and it is not allowed to have a load perpendicular to the plane of the lifting ring acting on it.

5) Set screw

Set screws are used to fix the relative position of the machine parts. Screw the set screw into the screw hole of the part to be tightened, and press its end against the surface of another part, that is, fix the former part on the latter part.

Set screws are usually made of steel or stainless steel, and their end shapes are tapered, concave, flat, cylindrical, and stepped. The end of the tapered or concave end set screw directly tightens the part, which is generally used for places where it is not often disassembled after installation; the flat end set screw has a smooth end and does not damage the surface of the part after tightening. It is used for frequent adjustment of the position. Only small loads can be transmitted at the connection; the cylindrical end screw is used to adjust the fixed position frequently, it can withstand larger loads, but the anti-loosening performance is poor, and anti-loosing measures should be taken when fixing; Set screws are suitable for fixing parts with larger wall thickness.

6) Self-tapping screws

When the self-tapping screw is used on the connected part, the connected part does not need to be threaded in advance. When connecting, use screws to tap the threads directly. It is often used to join thin metal plates. There are two types of tapping screws with taper end and tapping screws with flat end.

7) Self-tapping lock screw

Self-tapping locking screws not only have self-tapping effect, but also have low screw-in torque and high locking performance. Its thread has a triangular cross-section, and the surface of the screw is hardened and has high hardness. Its thread specifications are M2~M12.

Nuts are with internal threaded holes, the shape is generally hexagonal column, there are also flat square column or flat cylinder, with bolts, studs or machine screws, used to fasten and connect two parts to make it a whole.

Nut types

Nut material: carbon steel, stainless steel, copper, alloy, etc.


The DISC-LOCK lock nut is composed of two parts, each part has a staggered cam, because the internal wedge design slope angle is greater than the bolt nut angle, this combination will be tightly bitten into a whole, when vibration occurs When, the convex parts of the DISC-LOCK anti-loosening nut are staggered to each other, generating lifting tension, so as to achieve a perfect anti-loosing effect.

 Lock-Nut specifications:

Nominal diameter
Flange diameter

Lock-Nut Applications:

  • Automobile industry-cars, trucks, buses
  • compressor
  • Construction machinery
  • Wind power equipment
  • agricultural machine
  • Foundry industry
  • Drilling equipment
  • Shipbuilding industry
  • military
  • Mining equipment
  • Oil drilling rig (onshore or offshore)
  • public facilities
  • Rail
  • Transmission system
  • Metallurgical equipment
  • Rock hammer

1. Ordinary tapping screws (thread forming tapping screws)

Ordinary self-tapping screws are the direct product of early sheet metal screws. The principle is: when it is screwed into the prefabricated hole, the internal thread connected with the screw is formed by displacing the material close to the hole and pushing the material into the gap between the threads.

2. Self-cutting and tapping screws (thread-cutting and tapping screws)

Because the thread forming of ordinary self-tapping screws is only quite thin. And it can be easily realized on materials with good toughness. The development of self-tapping screws has expanded the use of thicker cross-sections and harder, more brittle and other materials with poor deformability. In this way, a self-cutting and self-tapping screw is developed: a cutting groove or edge is machined at the end of the screw shaft. When this kind of screw is screwed into the prefabricated hole, the screw acts as a tap and actually cuts the thread connected with itself.

3. Self-extrusion and self-tapping screws (thread rolling and self-tapping screws)

In the early 1950s, fastener engineers began to realize the potential advantages of self-tapping screws as “structural”, not just attachments that bear light loads. This led to the development of a new type of self-tapping screw thread rolling self-tapping screw (self-extruding self-tapping screw). According to the design principle of cold forging forming taps, the thread and end are specially designed for this kind of screw, so that the screw can pass on the crest of the thread instead of on the side of the whole thread, and apply intermittent and periodic pressure to form Internal thread of connection. By concentrating and limiting the forming pressure, the compressed material close to the hole can flow more easily and better fill (squeeze) the flanks and bottoms of the self-tapping screw threads. Since the friction resistance of screwing in is much lower than that of ordinary self-tapping screws, threaded self-tapping screws (self-extruding and self-tapping screws) can be screwed into thicker sections. At the same time, it has better screwing control and tightening torque, and greatly improves the connection strength and overall firmness. The engineering standards for this kind of self-tapping screws stipulate that the selection of materials, heat treatment mechanical properties and work performance must be strictly controlled.

4. Self-drilling and tapping screws (self-drilling screws)

People have done statistics: among the ten items that make up the total assembly cost, the highest one includes hole processing. In practical applications, self-tapping screws need to machine pre-made holes. Moreover, in order to make the prefabricated holes have a good effect in practical applications, the size of these holes must be controlled within a fairly strict range. In the early 1960s, self-drilling and self-tapping screws appeared. Since there is no need to process pre-made holes, it is a big step forward to reduce assembly costs. In a nutshell, self-drilling and self-tapping screws realize one operation of drilling, tapping and tightening.

Self-tapping screws                                                                      Self-tapping screws

Although there are many types of self-tapping screws, they all have the following points in common:

  • (1) Generally, it is made of carburized steel (accounting for 99% of the total output). It can also be made of stainless steel or non-ferrous metals.
  • (2) The product must undergo heat treatment. Carbon steel self-tapping screws must be carburized, and stainless steel self-tapping screws must be solid solution hardened. In order to make the self-tapping screw meet the mechanical properties and use performance required by the standard.
  • (3) The product has high surface hardness and good core toughness. That is “soft inside and rigid outside.” This is a major feature of the performance requirements of self-tapping screws. If the surface hardness is low, it cannot be screwed into the matrix; if the core has poor toughness, it will break when screwed and cannot be used. Therefore, the “inner flexible outer steel” is a self-tapping screw that satisfies the use performance, which is a very important requirement.
  • (4) The surface of the product needs surface protection treatment, generally electroplating treatment. The surface of some products must be phosphated (phosphated), such as wallboard self-tapping screws are mostly phosphated.
  • (5) It is produced by cold heading process. It is recommended to use high-speed cold heading machine and high-speed thread rolling machine or high-speed planetary thread rolling machine for production. High speed is emphasized here to ensure product quality. Only the heads of self-tapping screws produced by high-speed machines are well formed and the thread quality is high.
In general, the size, mechanical properties and working performance requirements of self-tapping screws have the following standards:
1. Self-tapping screw size standard
The ASME B18.6.3 2010 standard not only introduces the dimensions of slotted and cross recessed self-tapping screws and metal drive screws, but also includes the mechanical properties and working performance requirements of carbon steel self-tapping screws. The appendix gives instructions for measuring various sizes and application guidance on clamping length and test aperture.
2. Self-tapping screw performance standards (including mechanical properties and working performance):
(1) SAE J933: introduces the mechanical properties and working performance requirements of carbon steel ordinary self-tapping screws and white-cut self-tapping screws. It further specifies the requirements for the selection of raw materials, heat treatment, the depth of the carburized layer, surface hardness, and core hardness.
(2) SAE J81: introduces the mechanical properties and working performance of self-extrusion and self-tapping screws (self-tapping locking screws).
(3) SAE J78: introduces the mechanical properties and working performance of self-drilling and self-tapping screws.
(4) IFl-113: introduced the mechanical properties and working performance of self-drilling and self-tapping screws.
(5) ASTM C1513: introduces the mechanical properties and performance requirements of carbon steel self-tapping screws.
For other special types of self-tapping screws, there are no corresponding national standards or industrial standards, and no data for self-tapping screws made of other metal materials other than carbon steel are recognized. For the technical data of these self-tapping screws, you can consult the manufacturer.

Wood screws are similar to machine screws, but the thread on the screw is a special wood screw thread, which can be directly screwed into the wooden component (or part) to connect a metal (or non-metal) part with a through hole to a wooden The components are firmly connected together. This connection is also a detachable connection.

wood screws sizes                                                         wood screws sizes


Wood screws are the most frequently used woodworking fasteners. They are used primarily for connecting wood to wood and are known for the clamping force that they provide to strengthen a joint. They are also used to attach hardware, hinges, locks and other items to wood.


For wood screws, one section is a polished rod, and the thread angle and pitch of wood screws are different from those of self-tapping.

Self-tapping screws have high hardness, wide thread spacing, deep threads, and non-smooth surface. Wood screws are the opposite. The other difference is more obvious. There is no thread in the back section of wood screws. Self-tapping screws generally have to undergo heat treatment, and wood screws are not needed. The concept of self-tapping screws is actually very general, because there are many different types of heads.

The purpose of wood screws: similar to machine screws, but the thread on the screw is a special rib for wood screws, which can be screwed directly into the wood components (or parts).

Washers are divided into: flat washers-C level, large washers-A and C levels, extra large washers-C level, small washers-A level, flat washers-A level, flat washers-chamfered type-A level, high for steel structure Strength washers, spherical washers, tapered washers, square bevel washers for I-beam steel, square bevel washers for channel steel, standard spring washers, light spring washers, heavy spring washers, internal tooth lock washers, internal serrated lock washers, External tooth lock washers, external serrated lock washers, single-ear stop washers, double-ear stop washers, outer tongue stop washers, and stop washers for round nuts.

Flat washers are generally used in connecting parts, one is soft and the other is hard and brittle. Its main function is to increase the contact area, disperse the pressure, and prevent the soft texture from being crushed. The basic function of the spring of the spring washer is to give a force to the nut after tightening the nut to increase the friction between the nut and the bolt! The material is 65Mn (spring steel), the heat treatment hardness is HRC44~51HRC, and the surface is oxidized.

Anti-loosening washer Anti-loosening washer washer (spring) washer, circlip is a flexible cushion or card anti-loosening washer, a washer that prevents bolts from loosening. The working principle of the lock washer is very simple. It consists of two washers. The outer side is a radial convex surface, and the inner side is a helical tooth surface. When assembling, the inner helical tooth surfaces are opposed to each other, and the outer radial convex surface is in occlusal state with the contact surfaces at both ends. When the connecting piece is vibrated and the bolt tends to loosen, only the inner helical tooth surfaces of the two washers are allowed to face each other. Mismovement generates lifting tension, so as to achieve 100% locking.

Spring washers are widely used in load-bearing and non-load-bearing structures of general mechanical products. They are characterized by low cost, convenient installation, and suitable for parts with frequent assembly and disassembly. The automatic selection of washers is included, but the anti-loosening ability of spring washers is very low! Especially in European and American countries that require high reliability products, the adoption rate is extremely low, especially the important load-bearing structural connection parts have long been abandoned. Our country still has some applications in military industry, but it has been improved to stainless steel. The use of steel spring washers has long been banned in CASC! It is also said to be very unsafe. There are two reasons: 1 is “bulging ring” and 2 is hydrogen embrittlement.

Spring washers are often called spring washers in the screw industry. Its materials are stainless steel and carbon steel, and carbon steel is also iron. Commonly used spring washers are M3, M4, M5, M6, M8, M10, M12, M14, M16. These specifications are more commonly used.

It can be installed in the shaft groove or hole groove of the machine and equipment to prevent the parts on the shaft or hole from moving left and right.

Mainly used for parts positioning, and some can also be used for connecting parts, fixing parts, transmitting power or locking other fasteners


A type of fastener composed of two parts, a head and a nail rod, is used to fix and connect two parts with through holes to make them into a whole. This type of connection is called a rivet connection. It is a non-detachable connection, because in order to separate the connected parts, the rivets on the parts must be broken.


Assembly refers to a type of fastener supplied in combination, such as a combination of a certain machine screw (or bolt, self-tapping screw) and a flat washer (or spring washer, lock washer); the connection sub refers to a special bolt, A type of fastener supplied by a combination of nut and washer, such as a high-strength large hexagonal head bolt connection pair for steel structure

A type of fastener composed of nail rod and nail head (or no nail head), which is fixedly connected to a part by welding, so as to be connected with other parts

Author: Mose Li

Author: Mose Li

Director of Project Engineering at 3Q Machining

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