Standard fasteners are divided into twelve categories, and the selection is determined according to the use occasions and functions of the fasteners.
1. Bolts: Bolts are widely used in detachable connections in mechanical manufacturing, and are generally used in conjunction with nuts (usually plus a washer or two washers).
2. Nuts: Nuts are used in conjunction with bolts.
3. Screws: Screws are usually used alone (sometimes with washers), generally for tightening or tightening, and should be screwed into the internal thread of the body.
4. Studs: Studs are mostly used to connect one of the connected parts with a large thickness and need to be used in places where the structure is compact or the bolt connection is not suitable due to frequent disassembly. Studs are generally threaded at both ends (single-ended studs are threaded on one end). Usually, one end of the thread is firmly screwed into the body of the component, and the other end is matched with the nut, which plays the role of connection and tightening, but in the To a large extent also has the role of distance.
5. Wood screws: Wood screws are used to screw into wood for connection or fastening.
6. Self-tapping screws: The working screw holes that match the self-tapping screws do not need to be tapped in advance. When the self-tapping screws are screwed in, the internal thread is formed.
7. Washers: Washers are used between the bearing surfaces of bolts, screws and nuts and the workpiece bearing surface to prevent loosening and reduce the stress on the bearing surface.
8. Retaining ring: The retaining ring is mainly used to position, lock or stop the parts on the shaft or in the hole.
9. Pins: Pins are usually used for positioning, but also for connecting or locking parts, and as overload shearing elements in safety devices.
10. Rivet: One end of the rivet has a head, and the stem has no thread. 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 pair 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 rotate freely on the screw (or bolt) without falling off. Mainly play the role of tightening or tightening.
12. Others Mainly include welding studs and so on.
(1) Principles of selection of varieties
① Considering the efficiency of processing and assembling, in the same machinery or project, the variety of fasteners used should be minimized;
②From economic considerations, the variety of commodity fasteners should be preferred.
③According to the expected use requirements of fasteners, the selected varieties are determined in terms of type, mechanical properties, precision and thread.
a) General purpose bolts: There are many varieties, including hexagonal head and square head. Hexagon head bolts are the most common application, and are divided into A, B, C and other product grades according to manufacturing accuracy and product quality, with A and B grades being the most widely used, and are mainly used for important, high assembly accuracy and those subject to greater impact, vibration or where the load changes. Hexagon head bolts can be divided into two types: hexagonal head and large hexagonal head according to the size of the head support area and the size of the installation position; the head or screw has a variety with holes for use when locking is required. The square head of the square head bolt has a larger size and a stress surface, which is convenient for the wrench mouth to be stuck or lean against other parts to prevent rotation. Loose adjustment position in slot. See GB8, GB5780～5790, etc.
b) Bolts for reaming holes: when in use, the bolts are tightly inserted into the reaming holes to prevent the dislocation of the workpiece, see GB27, etc.
c) Anti-rotation bolts: There are square neck and tenon, see GB12~15, etc.;
d) Special purpose bolts: including T-slot bolts, joint bolts and anchor bolts. T-slot bolts are mostly used in places that need to be disconnected frequently; 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 hoisting machinery, see GB3632, etc.
a) General purpose nuts: There are many varieties, including hexagonal nuts, square nuts, etc. Hexagon nuts and hexagon bolts are most commonly used, and are classified into product grades A, B, and C according to manufacturing accuracy and product quality. Hexagonal thin nuts are used as auxiliary nuts in anti-loosening devices, which play a locking role, or are used in places where the threaded connection pair is mainly subjected to shearing force. Hexagonal thick nuts are mostly used in connections that are frequently disassembled. The square nut is matched with the square head bolt, and the wrench is not easy to slip, and it is mostly used for rough and simple structures. See GB41, GB6170～6177, etc.;
b) Slotted nut: mainly refers to the hexagonal slotted nut, that is, a groove is machined above the hexagonal nut. It is used in conjunction with screw bolts with holes and cotter pins to prevent the bolts and nuts from rotating relative to each other, see GB6178-6181, etc.;
c) Lock nut: refers to the nut with locking function, including nylon insert hexagonal lock nut and all-metal hexagonal lock nut. Hexagonal nylon ring lock nut has a very reliable anti-loosening ability. Under the operating temperature of -60 ~ +100 ℃ and certain medium conditions, it has the advantages of not damaging the bolts and the connected parts, and can be frequently loaded and unloaded. See GB889, GB6182～6187, etc.;
d) Nuts for special purposes: such as wing nuts, cap nuts, knurled nuts and insert nuts, etc. Wing nuts can generally be disassembled and assembled without tools, and are usually used in places that need to be disassembled frequently and are not subject to much force; cap nuts are used in places where the end screw needs to be covered. See GB62, GB63, GB802, GB923, GB806, GB807, GB809, etc.
a) Machine screws: They are divided into many varieties due to different head shapes and groove shapes. There are three types of head types: cylindrical head, pan head, countersunk head and semi-sunk head. The cross recessed screw has good neutrality when screwing, and the head strength is larger than that of the slotted one, and it is not easy to be bald. It is generally used in mass production. Hexagon socket head cap screws and socket head socket head cap screws can apply a large tightening torque, have high connection strength, and the head can be embedded in the body. See GB65, GB67～69 and GB818～820, etc.;
b) Set screws: Set screws are used to fix the relative position of the parts, and the head has the type with slot, socket angle and square head. The square head can apply a large tightening torque, and the top tightening force is large, and it is not easy to be screwed. Slotted and hexagonal for easy sinking of parts. The end of the set screw is different according to the requirements of use. Generally, the most commonly used are three types: tapered end, flat end and cylindrical end. The taper end is suitable for parts with low hardness; when using a pointless taper end screw, a hole should be punched on the top surface of the part, and the taper surface should be pressed against the edge of the hole. The screw with the flat end at the end has a large contact area and does not damage the surface of the part after being tightened. The screw with the cylindrical end at the end does not damage the surface of the part, and is mostly used for fixing the parts mounted on the pipe shaft (thin-walled part). . 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 embedded, see GB70, GB6190～6191 and GB2672～2674, etc.;
d) Screws for special purposes: such as positioning screws, non-prolapse screws and lifting eye screws, see GB72, GB828-829, GB837-839, GB948-949 and GB825, etc.
a) Unequal length studs: suitable for occasions where one end is screwed into the body of the component for connection or fastening, see GB897~900;
b) Equal length stud stud: suitable for matching with nuts at both ends for connection or distance. See GB901, GB953, etc.
Divided into many varieties due to different head shape and groove shape. There are several types of head, such as round head, countersunk head and semi-sink head.
a) Ordinary self-tapping screw: the thread conforms to GB5280, the pitch is large, and it is 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 ordinary metric coarse thread, suitable for use in applications requiring vibration resistance, see GB6560～6564.
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) washers: Spring washers rely on elasticity and oblique friction to prevent the loosening of fasteners, and are widely used in frequently disassembled connections. The inner tooth elastic washer and the outer tooth elastic washer have many sharp elastic warping teeth on the circumference, which are pressed against the supporting surface and can prevent the loosening of the fastener. The inner tooth elastic washer is used under the screw head with smaller head size; the outer tooth elastic washer is mostly used under the bolt head and the nut. The elastic washer with teeth is smaller than the ordinary spring washer, and the fastener is evenly stressed and reliable to prevent loosening, but it is not suitable for frequent disassembly. See GB93, GB859～860 and GB955;
c) Backstop washers: There are internal tooth lock washers, external tooth lock washers, single-ear stop washers, double-ear stop washers and stop washers for round nuts, etc. The single-ear and double-ear stop washers allow the nut to be tightened at any position to be locked, but the fastener should be close to the edge, see GB861~862, GB854~855, GB858, etc.;
d) Oblique washer: In order to adapt to the inclination of the working bearing surface, an oblique washer can be used. Square inclined washers are used to flatten the inclined surfaces such as channel steel and I-beam flanges, so that the bearing surface of the nut is perpendicular to the nail rod, so as to avoid the bending force of the screw rod when the nut is tightened. See GB852 ~ 853 and so on.
⑧ Retaining ring
a) Retaining ring: The elastic retaining ring for shaft and hole is clamped in the shaft groove or hole groove for the rolling bearing to be installed and back-stopped. In addition, there is an open retaining ring for the shaft, which is mainly used to be clamped in the shaft groove as a part It is used for positioning, but cannot bear axial force. See GB893～894 and GB896;
b) Wire retaining ring: wire retaining ring and wire locking ring with holes (for shaft). The steel wire retaining ring can also bear a certain axial force when it is installed in the shaft groove or hole groove for part positioning. See GB895.1～.2, GB921;
c) Locking retaining rings for shaft parts: retaining rings locked with taper pins and retaining rings locked with screws are mainly used to prevent the 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.
a) Cylindrical pins: Cylindrical pins are mostly used to fix parts on the shaft, transmit power, or act as positioning elements. Cylindrical pins have different diameter tolerances for different fit requirements. Cylindrical pins are generally fixed in the holes by interference, so they should not be disassembled too much. See GB119～120, GB878～880, etc.;
b Cone pin: The taper pin has a taper of 1:50, which is easy to install to the eye and can also ensure self-locking. It is generally used as a positioning element and a connecting element, and is mostly used in places that require frequent disassembly. Internally threaded taper pins and threaded tail taper pins for use in holes that do not pass through or in holes where it is difficult to drive a pin. The end of the split tapered pin can be opened after being driven into the hole, preventing the pin itself from slipping out of the hole. See