The selection of fasteners is in principle

Although many screw people know the category, shape, design, etc. of fasteners very well, the eager «screw man» has been looking for more comprehensive knowledge points.
First, determine the category
Standard fasteners are divided into ten categories. The selection should be based on the use of standard fasteners and their use.
1 Bolt: Bolts are generally matched with nuts (usually with a washer or two washers) for connection and fastening purposes.
3 Screws: Screws are usually used separately (sometimes with a washer) and are generally tightened or tightened.
4 Studs: Studs are generally threaded at both ends (single-headed studs are single-ended with threads). Usually, a rib is firmly screwed into the part body, and the other end is matched with the nut to connect and fasten. But to a large extent also has the role of distance.
6 Self-tapping screws: The workpiece screw holes matched with the self-tapping screws do not need to be tapped beforehand. When the self-tapping screws are screwed in, the internal threads are formed.
7 rivets: The rivet has a head at one end and the stem is unthreaded. 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.
8 pin: The pin is inserted into the workpiece during use, usually for connection or positioning.
9 retaining ring: The retaining ring is usually on the shaft or in the hole to limit the axial direction of the workpiece.
10 wood screws: Wood screws are used to screw into the wood for connection or fastening.
1. The principle of selection of varieties:
(1) Considering the work efficiency of processing and assembly, the types of standard parts should be minimized in the same machinery or engineering.
(3) According to the expected use requirements of the standard parts, the selected varieties are determined according to the type, mechanical properties, precision and thread.
2, type:
(1) Bolt: (Introduction: Selection of bolts in mechanical design)
1 General purpose bolts: There are many varieties, there are hexagonal heads and square heads.
2 Bolts for reaming holes: When used, the bolts are tightly fitted into the holes made by the hinges to prevent the workpiece from being misaligned.
3 stop bolt: There are square neck, with the division of the vertebra.
4 special purpose bolts: such as T-slot bolts, see GB37; joint bolts, see GB798; anchor bolts.
5 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) Nut:
1 general purpose nut: mainly refers to hex nut, and other square nuts, many varieties, see GB41, GB6170-6177 and so on.
2 slotted nut: mainly refers to the hexagonal slotted nut, that is, it is processed out of the hex nut. It is used with screw bolts and split pins to prevent relative rotation of bolts and nuts. See GB6178-6181.
3 lock nut: refers to the nut with locking function, nylon insert hexagonal lock nut, see GB889, GB6182, GB6183 and all metal hexagon lock nut, see GB6184-6187.
4 special purpose nuts: such as disc nut, see GB62; ring nut, see GB63; cap nut, see GB802, GB923; knurled nut, see GB806, GB807 and embedded nuts, see GB809.
(3) Screw:
1 Machine screw: It is divided into many varieties depending on the head type and the groove type. The head type has a cylindrical head, a pan head, a countersunk head and a semi-recessed head, and the head is shaped into a slot (a word) and a cross slot. See GB65, GB67-69 and GB818-820.
2 set screw: The set screw uses its tail end to prevent mutual displacement between the workpieces and to transmit less torque. See GB71, GB73-75, GB77, GB78, etc.
3 Hexagon socket head cap screws: Hexagon socket head cap screws are suitable for applications where the installation space is small or the head of the screw needs to be buried. See GB70, GB6190, GB6191 and GB2672-674.
4 special purpose screws: such as positioning screws, see GB72, GB828, GB829; do not pull out the screws, see GB827-839, GB948, GB948 and eyebolts, see GB825.
(4) Stud:
1 unequal long stud: It is suitable for the case where one end is screwed into the component body for connection or fastening. See GB897-900 and so on.
2 equal length studs: suitable for matching the ends with nuts, for connecting or spacing. See GB901, GB953, etc.
(5) Washer:
1 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.
2 spring (elastic) washers: see GB93, GB859, etc. for spring washers, GB860, GB955, etc. for elastic washers.
3 anti-return washer: with internal tooth lock washer, see GB861; external tooth lock washer, see GB862; single-ear stop washer, see GB854; double-ear stop washer, see GB855; round nut stop washer, see GB858 Wait.
4 oblique washer: In order to adapt to the slope of the workpiece support surface, a diagonal washer can be used. For square slanted washers with I-beams, see GB852; for square slanted washers for channel steel, see GB853.
(6) Self-tapping screws:
1 Ordinary self-tapping screws: thread conforms to GB5280 (thread for self-tapping screws), large pitch, suitable for use on thin steel plates or copper, aluminum, plastic. See GB845-847, GB5282-5284, etc.
2 Self-tapping locking screw: The thread conforms to the ordinary metric coarse thread and is suitable for use in vibration resistant situations. See GB6560-6564.
(7) Rivets:
1 hot forging rivets: general specifications are large, mostly used in locomotives, ships and boilers, etc., usually need to be shaped by hot forging. See GB863-866.
2 cold head forming rivets: general diameter specifications ≤ 16mm, usually formed by cold heading. See GB867-870, GB109, etc.
3 hollow and semi-tubular rivets: hollow rivets, see GB976; semi-tubular rivets, see GB873-875 and so on.
4 special purpose rivets: with or without head rivets, see GB1016; tubular rivets, see GB975; sign rivets, see GB827 and so on.
1 cylindrical pin: with or without threaded cylindrical pin, see GB119; internal threaded cylindrical pin, see GB120; externally threaded cylindrical pin, see GB878; elastic cylindrical pin, see GB879; perforated cylindrical pin, see GB880.
2 taper pin: with or without threaded cylindrical pin, see GB117; internal threaded cylindrical pin, see GB118; screw tail taper pin, see GB881; open taper pin, see GB877.
3 cotter pin: generally matched with the screw hole bolt and the slotted nut to prevent the bolt and nut from loosening. See GB91.
(9) retaining ring:
1 circlip: circlip with holes. See GB893; circlip with shaft. See GB894 and the shaft retaining ring GB896.
2 wire retaining ring: wire retaining ring with holes, see GB895.1; wire retaining ring for shaft, see GB895.2 and wire lock ring, see GB921.
Locking ring for 3-axis type parts: retaining ring with tapered pin lock, see GB883; retaining ring with screw, see GB884, GB885, etc.
4-axis end retaining ring: shaft end retaining ring with screw fastening, see GB891 and shaft end retaining ring bolted, see GB892.
(10) Wood screws:
It is divided into many varieties depending on the head shape and the groove type. 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, etc.
Third, the mechanical performance level
(1) Bolts, screws, studs and nuts
Ordinary self-tapping screws are not classified according to mechanical properties. As long as the appropriate specifications are selected, see 3.6 and 3 in GB3098.5 to meet their general requirements.
The mechanical performance grade of self-tapping locking screws is divided into two levels, A and B. Class A is a high strength class; Class B is a low strength class.
Fourth, accuracy
Table: Product grade and accuracy of standard parts (fasteners)
Five, thread
Determine specifications
1 Diameter specifications Try to select the first series of values, as far as possible not to use the values in the brackets in the product standard size table and the values in the specification table that should not be used.
2 Length specifications generally do not use specifications other than those specified in the product standard. When the bolt or nut is normally connected, the length of the thread end is preferably (0.2-0.3) d.
3 The size and length of the matching specifications should be preferred within the specifications of the product specifications.