The three concepts of bolt, screw and screw

In life, bolts, screws, screws, etc. are often mentioned. What is the difference between them? In fact, the standard argument is that there are no screws or nuts. Screws are commonly known as screws with external threads. The shape of the nut is usually hexagonal, and the inner hole is an internal thread, which is used to cooperate with the bolt to tighten the related parts. Nuts are commonly known, and the standard should be called "nuts". The head of the bolt is generally hexagonal, and the shaft has external threads. The screw is small, the head has a flat head, cross head, etc., and the shaft has an external thread. The studs should actually be called "double-ended studs". Both ends have external threads, and the middle is generally a smooth rod. The long end of the thread is used to connect with the deep hole, and the short end is connected with the nut.
Standard fasteners are divided into twelve categories, and the selection is based on the use of the fastener and its function.
1. Bolt
Bolts are widely used in detachable connections in mechanical manufacturing, and are generally used in conjunction with nuts (usually plus one washer or two washers).
2. Nut
3. Screws
The screw is usually used alone (sometimes with a washer), generally used for fastening or tightening, and should be screwed into the internal thread of the body.
4. Stud
Studs are mostly used to connect one of the connected parts with a large thickness, which needs to be used in a compact structure or because it is frequently disassembled and it is not suitable to use bolt connection. Studs are generally threaded at both ends (single-end studs are threaded at one end), usually one thread is screwed into the body of the component, and the other end is matched with the nut to play the role of connection and fastening, but it is very To a large extent, it also has the function of setting a distance.
5. Wood screws
Wood screws are used to screw in wood for connection or fastening.
6. Self-tapping screws
The working screw hole matched with the self-tapping screw does not need to be tapped in advance. While screwing in the self-tapping screw, the internal thread is formed.
7. Washer
The washer is used between the supporting surfaces of bolts, screws, nuts, etc. and the supporting surface of the workpiece to prevent loosening and reduce the stress on the supporting surface.
8. Retaining ring
The retaining ring is mainly used to position, lock or stop the part on the shaft or in the hole.
9. Sell
Pins are usually used for positioning, they can also be used to connect or lock parts, and can also be used as overload shearing elements in safety devices.
10. Rivets
The rivet has a head at one end and the shank has no threads. When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is riveted for connection or fastening.
11. Connection Vice
The connection pair is a combination of screws or bolts or self-tapping screws and washers. After the washer is installed on the screw, it must be able to turn freely on the screw (or bolt) without falling off. Mainly play the role of fastening or tightening.
12. Other
Mainly includes welding nails and other content.
Determine variety
(1) The principle of variety selection
① Considering the working efficiency of processing and assembly, within the same machine or project, the variety of fasteners should be minimized;
② For economic considerations, priority should be given to varieties of commodity fasteners.
③ According to the expected use requirements of fasteners, determine the selected varieties according to the type, mechanical properties, precision and thread.
(2) Type
① Bolt
a) General-purpose bolts: there are many varieties, with hexagonal head and square head. Hexagon head bolts are the most common applications. They are divided into A, B, C and other product grades according to manufacturing accuracy and product quality. A and B grades are the most used. They are mainly used for important, high-precision assembly, and subject to large impact, vibration or Variable load place. Hexagon head bolts can be divided into hexagonal heads and large hexagonal heads according to the size of the head support area and the installation position; the head or screw has holes for the need to lock. The square head of the square head bolt has a large size and a force-bearing surface, which is convenient for the wrench mouth to catch or lean against other parts to stop rotation. It is commonly used on relatively rough structures, and sometimes used in T-slots to facilitate the bolt in Loosely adjust the position in the slot. See GB8, GB5780～5790, etc.
b) Bolts for reaming holes: insert the bolts tightly into the reaming holes during use to prevent the workpiece from being misaligned, see GB27, etc.
c) Anti-rotation bolt: It has square neck and tenon, see GB12～15, etc.;
d) Special purpose bolts: including T-slot bolts, articulated bolts and anchor bolts. T-slot bolts are mostly used in places where the connection needs to be frequently disassembled; anchor bolts are used to fix the frame or motor base in the cement foundation. See GB798, GB799, etc.;
e) High-strength bolt connection pair for steel structure: generally used for friction-type connection of steel structures such as buildings, bridges, towers, pipeline supports and lifting machinery, see GB3632, etc.
② Nut
a) General-purpose nuts: there are many varieties, including hexagon nuts and square nuts. Hex nuts and hex bolts are most commonly used, and are classified into A, B, and C grades according to manufacturing accuracy and product quality. Hexagonal thin nuts are used as secondary nuts in anti-loosening devices to play a locking role, or where the threaded joints mainly bear shear forces. Thick hexagon nuts are mostly used in connections that are frequently disassembled. Square nuts and square head bolts are used together, the wrench is not easy to slip, it is mostly used for rough and simple structure. See GB41, GB6170～6177, etc.;
b) Slotted nut: mainly refers to the hexagonal slotted nut, that is, the slot is processed above the hexagonal nut. It is used in conjunction with bolts with holes and cotter pins to prevent relative rotation of bolts and nuts, see GB6178～6181, etc.;
c) Lock nut: refers to a nut with a locking function, including nylon insert hexagon lock nuts and all-metal hexagon lock nuts, etc. The hexagonal nylon ring lock nut has a very reliable anti-loosening ability. It has the advantages of not damaging the bolts and the connected parts, and can be frequently loaded and unloaded under the use temperature of -60 ~ +100 ℃ and a certain medium. See GB889, GB6182～6187, etc.;
d) Special-purpose nuts: such as butterfly nuts, cap nuts, knurled nuts, and embedded nuts. Butterfly nuts can generally be disassembled without tools, and are usually used in places that need to be frequently disassembled and have little stress; cover nuts are used where the end screws need to be covered. See GB62, GB63, GB802, GB923, GB806, GB807, GB809, etc.
③ Screw
a) Machine screws: Divided into many varieties due to different head shape and groove shape. The head type includes a cylindrical head, a pan head, a countersunk head and a semi countersunk head. The head groove is generally slotted (slotted), cross groove and internal hexagonal groove. The cross-slotted screws have good neutrality when they are screwed, the head strength is greater than that of the slotted grooves, and they are not easy to be bald. They are generally used in mass production. Hexagon socket head cap screws and hexagon socket head cap screws can apply a large tightening torque, and the connection strength is large. The head can be buried in the machine body. It is used for the joints that require compact structure and smooth appearance. See GB65, GB67～69 and GB818～820 etc.;
b) Set screw: The set screw is used to fix the relative position of the parts. The head has a slotted, hexagonal and square head type. The square head can apply a large tightening torque, the top tightening force is large, and it is not easy to screw the bald head, but the head size is large, it is inconvenient to be buried in the parts, and it is not safe, especially for moving parts. Slotted and hexagon sockets are easy to sink into parts. According to the different requirements of the set screw end, the most commonly used are the tapered end, the flat end, and the cylindrical end. The tapered end is suitable for parts with low hardness; when using a non-pointed tapered end screw, a hole should be punched on the top surface of the part, and the cone surface is pressed against the edge of the hole. The screw with a flat end at the end has a large contact area and does not hurt the surface of the part after tightening. It is used for tightening a flat surface with greater hardness or frequently adjusting the position. The screw with the cylindrical end does not damage the surface of the part. It is mostly used to fix the part mounted on the tube shaft (thin-walled part). The cylindrical end is pushed into the hole on the shaft. The shear resistance of the round end 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 screw head needs to be buried, see GB70, GB6190～6191 and GB2672～2674, etc.;
d) Screws for special purposes: such as set screws, unscrewed screws and eye bolts, see GB72, GB828～829, GB837～839, GB948～949 and GB825.
④　 stud
a) Double-headed studs of unequal length: suitable for occasions where one end is screwed into the component body for connection or fastening, see GB897～900;
b) Double-headed studs of equal length: suitable for connecting or fixing the distance with the nuts at both ends. See GB901, GB953, etc.
⑤　Wood screws
Because of the different head shape and groove shape, it is divided into many varieties. There are several types of heads, such as round head, countersunk head, and semi countersunk head. The head grooves are slotted (slotted) and cross grooved. See GB99～101, GB950～952.
⑥Self-tapping screws
a) Ordinary self-tapping screws: the thread conforms to GB5280, the pitch is large, suitable for use on thin steel plate or copper, aluminum, plastic, see GB845～847, GB5282～5284, etc.;
b) Self-tapping locking screw: The thread conforms to the common metric coarse thread, suitable for use in vibration-resistant occasions, see GB6560～6564.
⑦washer
a) Flat washer: used 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) washer: The spring washer is used to prevent loosening of fasteners due to the elasticity and friction of the oblique opening. It is widely used for frequently disassembled connections. The inner tooth elastic washer and the outer tooth elastic washer have a lot of sharp elastic warped teeth on their circumference, which puncture the bearing surface and can prevent the fastener from loosening. Internal tooth elastic washers are used under screw heads with small head sizes; external tooth elastic washers are mostly used under bolt heads and nuts. The toothed elastic washer is smaller than the ordinary spring washer, and the fasteners are evenly loaded and reliable to prevent loosening, but they are not suitable for frequent disassembly. See GB93, GB859～860 and GB955;
c) Anti-return washer: there are internal tooth lock washer, external tooth lock washer, single-ear stop washer, double-ear stop washer and round nut stop washer, etc. Single-ear and double-ear stop washers allow the nuts to be tightened and locked at any position, but the fasteners should be close to the edge, see GB861～862, GB854～855, GB858, etc.;
d) Inclined washer: In order to adapt to the inclination of the working bearing surface, an inclined washer can be used. Square inclined washers are used to flatten inclined surfaces such as channel steel and I-shaped steel flanges, so that the nut support surface is perpendicular to the nail rod, to avoid bending forces on the screw when the nut is tightened. See GB852～853 etc.
⑧ Retaining ring
a) Retaining ring: Retaining rings for shaft and hole are stuck in the shaft groove or hole groove for rolling bearing after installation, and there are also open retaining rings for shaft, which are mainly used to be stuck in the shaft groove for parts Used for positioning, but cannot withstand axial force. See GB893～894 and GB896;
b) Wire retaining ring: Wire retaining ring and wire locking ring for holes (for shaft). The wire retaining ring is installed in the shaft groove or hole groove for positioning of parts, and can also bear a certain axial force. See GB895.1～.2, GB921;
c) Locking retaining ring for shaft parts: Retaining ring with conical pin lock and retaining ring with screw lock are mainly used to prevent axial movement of parts on the shaft. See GB883～892.
d) Shaft end retaining ring: The shaft end retaining ring fastened with screws and the shaft end retaining ring fastened with bolts are mainly used to lock the parts fixed on the shaft end. See GB883～982.
⑨ pin
a) Cylindrical pins: Cylindrical pins are mostly used for fixing parts on the shaft, transmitting power, or as positioning elements. Cylindrical pins have different diameter tolerances and can be used for different matching requirements. Cylindrical pins are generally fixed in the holes by interference, so it is not appropriate to disassemble them. See GB119～120, GB878～880, etc.;
b Tapered pin: The tapered pin has a taper of 1:50, which is convenient for installation and alignment, and can also ensure self-locking. It is generally used as a positioning element and a connecting element, and is often used in places where frequent disassembly is required. The internally threaded tapered pin and the threaded tail tapered pin are used for holes that do not penetrate or for holes where it is difficult to punch out the pin. After the open-end conical pin is driven into the hole, the end can be opened to prevent the pin from sliding out of the hole. See GB117～118, GB881 and GB877 etc.
The pin holes of cylindrical pins and various conical pins generally need to be processed through reaming. After repeated assembly and disassembly, the positioning accuracy and connection tightening will be reduced, and only a small load can be transmitted. The elastic cylindrical pin itself has elasticity, maintains tension in the hole, is not easy to loosen, is easy to disassemble, and does not affect the matching nature, and the pin hole does not need to be hinged. Pins and pins with holes are used for hinged joints;
c) Cotter pin: The cotter pin is an anti-loosening device that connects the machine parts. When used, it penetrates into the nut, bolt with pin hole or other connector pin holes, and then separates the feet. See GB91.
⑩Rivet
a) Hot forging forming rivets: The general specifications are large, and they are mostly used for locomotives, ships and boilers. Usually, the head is formed by hot forging, see GB863~866;
b) Cold heading rivets: The general diameter is 16mm, and the head is usually formed by cold heading, see GB867～870, GB109, etc.
c) Hollow and semi-hollow rivets: Hollow rivets are used in places where there is little shear force, and are often used to connect non-metal parts such as plastic, leather, wood, canvas and so on.

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