What are the differences between bolts, screws and studs?

In life, bolts, screws, nuts are often mentioned. What are the differences between them? In fact, the standard is that there are no screws and nuts. Screws are commonly known as “screws” with external threads. The shape of the nut is usually hexagonal, and the inner hole is internally threaded to match the bolt and tighten the relevant parts. The nut is a common name and the standard should be called “nut”. The head of the bolt is generally hexagonal and the stem has external threads. The screw is small, the head has a flat head, a crosshead, etc., and the stem has external threads. The stud should actually be called “double stud”, with external threads on both ends, and the middle is usually a polished rod. The long end of the thread is used to connect to the deep hole and the short one is connected to the nut.

Standard fasteners are divided into 12 categories, which are determined according to the use of fasteners and their functions.


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Bolts are widely used in mechanical construction for detachable connections and are typically used with nuts (usually with a washer or two washers).


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Screws are usually used separately (sometimes with washers) and are generally tightened or tightened and should be screwed into the internal threads of the body.


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Studs are often used to connect one of the connected parts to a large thickness, which requires a compact structure or a place where bolting is not necessary due to frequent disassembly. Studs are usually threaded at both ends (single-headed studs are single-ended with threads). Usually, one thread is screwed into the part body, and the other end is matched with the nut to connect and fasten, but it is very To a large extent, it also has the effect of spacing.

5、Wood screws

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Wood screws are used to screw into the wood for connection or fastening.

6、Self-tapping screws

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The working screw hole matched with the self-tapping screw does not need to be tapped in advance, and the internal thread is formed while the self-tapping screw is screwed.


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The washer is placed between the bearing surface of the bolt, the screw and the nut, and the workpiece supporting surface to prevent loosening and reduce the stress on the bearing surface.

8、Retaining ring

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The retaining ring is mainly used to position, lock or stop the part on the shaft or in the hole.


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Pins are often used for positioning, and can also be used to attach or lock parts, and can also be used as an overload shearing element in safety devices.


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The rivet has a head at one end and the stem is unthreaded. In use, the rod portion is inserted into the hole of the connected member, and then the end portion of the rod is riveted for connection or fastening.

Determine the variety
(1) Principles for selection of varieties
1 From the perspective of the efficiency of processing and assembly, the types of fasteners should be minimized in the same machinery or engineering;
2 For economic reasons, commodity fasteners should be preferred.
3 According to the expected use requirements of the fasteners, the selected varieties are determined according to the type, mechanical properties, precision and thread.
(2) Type
1 Bolt
a) General purpose bolts: There are many varieties, with hexagonal heads and square heads. Hexagon head bolts are the most common applications. They are classified into A, B, C and other product grades according to manufacturing precision and product quality. They are most used in Class A and Class B, and are mainly used for important, high assembly precision and subject to large shocks, vibrations or The place where the load is changed. Hexagon head bolts can be divided into hexagonal heads and large hexagonal heads according to their head support area and mounting position. The head or screw has a variety of holes for locking. The square head of the square head bolt has a larger size and a force-receiving surface, which is convenient for the wrench to be stuck or to resist the rotation of other parts. It is commonly used in relatively rough structures and sometimes in T-shaped grooves to facilitate the bolts. Loosen the position in the slot. See GB8, GB5780 ~ 5790 and so on.
b) Bolt for reaming hole: When using it, insert the bolt tightly into the reaming hole to prevent the workpiece from being misaligned, see GB27.
c) Stop bolt: There are square necks and belts, see GB12~15;
d) Special purpose bolts: including T-slot bolts, joint bolts and anchor bolts. T-slot bolts are often used in places where the joints need to be disconnected frequently; anchor bolts are used in fixed bases or motor bases in cement foundations. See GB798, GB799, etc.;
e) High-strength bolt connection for steel structure: Generally used for friction type connection of steel structures such as buildings, bridges, towers, pipe supports and lifting machinery, see GB3632.
2 Nuts
a) General purpose nuts: There are many varieties, such as hex nuts and square nuts. Hexagon nuts with hexagon bolts are the most common applications, and are classified into A, B, and C grades according to manufacturing precision and product quality. The hexagonal thin nut acts as a secondary nut in the lockout device, acts as a lock, or is used where the threaded connection is primarily subjected to shear forces. Hexagonal thick nuts are often used in connections that are often removed. The square nut is used with the square head bolt, the wrench is stuck and is not easy to slip, and is mostly used for a rough and simple structure. See GB41, GB6170~6177, etc.;
b) Slotted nut: mainly refers to the hex slotted nut, that is, the groove is machined above the hex nut. It is used with the screw with hole bolt and the split pin to prevent the bolt and the nut from rotating relative to each other, see GB6178~6181;
c) Lock nut: refers to the nut with locking function, nylon insert hexagon lock nut and all metal hexagon lock nut. The hexagonal nylon ring lock nut has a very reliable anti-loose ability. It has a little damage to the bolts and the connected parts and can be frequently loaded and unloaded under the use temperature of -60 to +100 ° C and certain media conditions. See GB889, GB6182~6187, etc.;
d) Special purpose nuts: such as wing nuts, cap nuts, knurled nuts and insert nuts. The wing nut can usually be disassembled without tools. It is usually used in places where it needs to be frequently disassembled and not stressed. The cap nut is used where the end screw needs a cover. See GB62, GB63, GB802, GB923, GB806, GB807, GB809, etc.
3 Screws
a) Machine screws: Divided into many varieties due to the difference in head shape and groove shape. The head type has a cylindrical head, a pan head, a countersunk head and a semi-recessed head. The head groove shape is generally a slotted (slotted groove), a cross slot and a hexagonal slot. When the Phillips screw is screwed, the neutrality is good, the strength of the head is larger than that of the slot, and it is not easy to be bald. It is generally used in mass production. Hexagon socket head cap screws and hexagon socket type screws can apply a large tightening torque. The connection strength is high and the head can be buried in the body for a compact and smooth joint. See GB65, GB67~69 and GB818~820;
b) Set screw: The set screw is used for the relative position of the fixed part. The head has a type of slotted, hexagonal and square head. The square head can apply a large tightening torque, the top tightening force is large, and it is not easy to be bald, but the head size is large, it is inconvenient to be buried in the part, and it is unsafe, especially the moving part is not suitable for use. The inner hexagon with a slotted groove makes it easy to sink into the part. The end of the set screw is usually the most commonly used, including the tapered end, the flat end and the cylindrical end. The tapered end is suitable for parts with low hardness; when using the tipless end screw, the hole is to be punched on the top surface of the part, and the cone is pressed on the side of the pit. The end of the flat end of the screw, the contact area is large, the top is not damaged after the surface of the part, used to tighten the hard surface or adjust the position frequently. The screw with the end of the cylinder end does not damage the surface of the part. It is often used to fix the parts mounted on the tube shaft (thin-walled part). The end of the cylinder end is inserted into the hole on the shaft. The round end is resistant to shearing and can transmit a large load. . See GB71, GB73-75, GB77-78, etc.;
c) Hexagon socket head cap screws: Hexagon socket head cap screws are suitable for occasions where the installation space is small or the head of the screw needs to be buried. See GB70, GB6190~6191 and GB2672~2674;
d) Special purpose screws: such as positioning screws, non-ejection screws and eyebolts, see GB72, GB828~829, GB837~839, GB948~949 and GB825.
4 Studs
a) unequal long studs: suitable for the occasion where one end is screwed into the body of the component for connection or fastening, see GB897-900;
b) Isometric double stud: It is suitable for the connection and the distance between the two ends and the nut. See GB901, GB953, etc.
5 Wood screws
It is divided into many varieties due to the difference in head shape and groove shape. The head type has a round head, a countersunk head, a semi-recessed head, etc., and the head groove shape is a slotted (slotted groove) and a cross recessed groove, see GB99-101, GB950-952.
6 Self-tapping screws
a) Ordinary self-tapping screws: thread conforms to GB5280, large pitch, suitable for use on thin steel plates or copper, aluminum, plastics, see GB845~847, GB5282~5284;
b) Self-tapping locking screw: The thread conforms to the common metric coarse thread, suitable for use in vibration resistant applications, see GB6560~6564.
7 Washer
a) Flat washer: to overcome the unevenness of the support surface of the workpiece and increase the stress area of the support surface, see GB848, GB95-97 and GB5287;
b) Spring (elastic) washers: Spring washers rely on elastic and oblique friction to prevent loosening of the fasteners and are widely used for frequently disassembled connections. The inner tooth elastic washer and the outer tooth elastic washer have a plurality of sharp elastic warping teeth on the circumference, and are pressed against the support surface to prevent the fastener from loosening. The internal toothed elastic washer is used under the screw head with a small head size; the external tooth elastic washer is mostly used under the bolt head and nut. The toothed elastic washer is smaller than the ordinary spring washer, and the fastener is evenly stressed and prevented from loosening, but it is not suitable for the frequent disassembly. See GB93, GB859~860 and GB955;
c) Stop washers: internal tooth lock washers, external tooth lock washers, single ear stop washers, double ear stop washers and retaining washers for round nuts. Single ear and double ear stop washers allow the nut to be tightened at any position for locking, but the fastener should be placed at the edge, see GB861~862, GB854~855, GB858, etc.;
d) Inclined washer: To accommodate the slope of the working bearing surface, a diagonal washer can be used. The square inclined washer is used to flatten the inclined surface such as the channel steel and the I-beam flange so that the nut supporting surface is perpendicular to the nail rod, so as to prevent the screw from being subjected to the bending force when the nut is tightened. See GB852~853 and so on.
8 Retaining ring
a) Retaining ring: The shaft and hole are clamped in the shaft groove or hole groove by the circlip and hole for the rolling bearing to be installed and then retracted. In addition, there is an opening ring for the shaft, which is mainly used for the part in the shaft groove. For positioning, but can not withstand axial forces. See GB893~894 and GB896;
b) Wire retaining ring: wire retaining ring (for shaft) and wire lock ring. The wire retaining ring is mounted in the shaft groove or the hole groove for a certain axial force when the component is positioned. See GB895.1~.2, GB921;
c) Locking ring for shaft parts: retaining ring with taper pin locking and retaining ring with screw, mainly used to prevent axial movement of parts on the shaft. See GB883~892.
d) Shaft end retaining ring: shaft end retaining ring with screw fastening and shaft end retaining ring fastened with bolts, mainly used to lock the parts fixed at the shaft end. See GB883~982.
9 Pin
a) Cylindrical pin: Cylindrical pin is mostly used for fixing parts on the shaft, transmitting power, or as a positioning component. Cylindrical pins have different diameter tolerances and can be used with different mating requirements. Cylindrical pins are generally fixed in the holes by interference, so it is not advisable to disassemble them. See GB119~120, GB878~880, etc.;
b Tapered pin: The taper pin has a taper of 1:50, which is easy to install to the eye, and can also be self-locking. It is generally used as a positioning component and a connecting component, and is often used in places where frequent disassembly is required. Internal thread taper pin and screw tail taper pin for non-through holes or for holes where it is difficult to punch. The open end taper pin is inserted into the hole and the end can be opened to prevent the pin itself from slipping out of the hole. See GB117~118, GB881 and GB877.
The pin holes of the cylindrical pin and various tapered pins generally need to be reamed. After repeated assembly and disassembly, the positioning accuracy and the fastening of the connection are reduced, and only a small load can be transmitted. The elastic cylindrical pin itself has elasticity, is installed in the hole to maintain tension, is not easy to loose, is easy to disassemble, and does not affect the mating property, and the pin hole does not need to be reamed. Perforated pin and pin, both for hinged joints;
c) Cotter pin: The cotter pin is a anti-loose device for connecting the mechanism. When using it, insert it into the pin hole of the nut, bolt with pin hole or other connecting piece, and then separate the foot. See GB91.
10 Rivets
a) hot forging rivets: general specifications are large, mostly used in locomotives, ships and boilers, etc., usually need to be formed by hot forging, see GB863 ~ 866;
b) Cold-formed rivets: generally 16mm in diameter, usually formed by cold heading, see GB867~870, GB109, etc.
c) Hollow and semi-tubular rivets: Hollow rivets are used for small shear forces and are commonly used to join non-metallic parts such as plastics, leather, wood, and canvas.

Source: China Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com


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