1. Determine the category
Standard fasteners are divided into ten categories. The selection should be determined according to the usage occasions and functions of the standard fasteners.
① Bolts: Bolts are generally matched with nuts (usually plus a washer or two washers) and are used for connection and tightening purposes.
② Nuts: Nuts and bolts are used together.
③Screws: Screws are usually used alone (sometimes with washers), and generally play a tightening or tightening role.
④ Studs: Studs are generally threaded on both ends (single-head 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 matches the nut. It plays the role of connecting and fastening, but to a large extent it also plays the role of distance.
⑤ Washers: Washers are placed between the supporting surfaces of bolts, screws, nuts, etc. and the process supporting surfaces to prevent loosening and reduce stress on the supporting surfaces.
⑥ Self-tapping screws: The screw holes of the workpiece that match the self-tapping screws do not need to be tapped in advance. The internal threads are formed while the self-tapping screws are screwed in.
⑦Rivet: The rivet has a head on one end and no threads on the stem. When in use, insert the rod into the hole of the connected piece, and then rivet the end of the rod to connect or tighten.
⑧Pin: The pin is embedded into the workpiece when used, and usually plays a connecting or positioning role.
⑨ Back-up ring: The back-up ring is usually on the shaft or in the hole and plays the role of limiting the axial direction of the workpiece.
⑩Wood screws: Wood screws are used to screw into wood for connection or fastening.
2. Determine standards and varieties
1. Principles for selecting varieties:
⑴Considering the work efficiency of processing and assembly, within the same machinery or project , the variety of standard parts used should be minimized.
⑵ From the perspective of economic considerations, priority should be given to the use of commercial standard parts.
⑶ According to the expected use requirements of standard parts, determine the selected varieties in terms of type, mechanical properties, accuracy and thread.
2. Type:
⑴ Bolts:
① General purpose bolts: There are many varieties, including hexagonal heads and square heads. See the national standard GB5780- GB5790 etc.
② Bolts for reamed holes: When used, insert the bolts tightly into the reamed holes to prevent the workpiece from being dislocated, see GB27, etc.
③ Anti-rotation bolt: There are square neck and vertebrae, see GB12-15, etc.
④Special purpose bolts: such as bolts for T-slots, see GB37; articulated bolts, see GB798; anchor bolts, see GB799, etc.
⑤ High-strength bolt connection pair for steel structures: generally used in friction-type connections of steel structures such as buildings, bridges, towers, pipe supports and lifting machinery, see GB3632, etc.
⑵ Nuts:
① General purpose nuts: mainly refers to hexagonal nuts, and there are also square nuts, with many varieties, see GB41, GB6170-6177, etc.
②Slotted nut: mainly refers to hexagonal slotted nut, that is, the slot is machined above the hexagonal nut. It is used in conjunction with screw hole bolts and cotter pins to prevent relative rotation of bolts and nuts, see GB6178-6181, etc.
③ Lock nut: refers to a nut with locking function, including nylon insert hexagonal lock nut, see GB889, GB6182, GB6183 and all-metal hexagonal lock nut, see GB6184-6187.
④ Special purpose nuts: such as dish nuts, see GB62; ring nuts, see GB63; cap nuts, see GB802, GB923; knurled nuts, see GB806, GB807 and embedded nuts, see GB809 wait.
⑶Screws:
①Machine screws: divided into many varieties due to different head types and groove types. The head types include cylindrical head, pan head, countersunk head and semi-countersunk head, and the head shapes are slotted (one-shaped material) and cross-slotted. See GB65, GB67-69 and GB818-820, etc.
② Set screw: The set screw uses its tail end to prevent mutual displacement between workpieces and transmit less torque. See GB71, GB73-75, GB77, GB78, etc.
③Hexagon socket head screws: Hexagon socket head screws are suitable for occasions where the installation space is small or the screw head needs to be buried. , see GB70, GB6190, GB6191 and GB2672-2674, etc.
④Special purpose screws: such as positioning screws, see GB72, GB828, GB829; non-detachment screws, see GB827-839, GB948, GB948 and eye screws, see GB825, etc.
⑷Studs:
①Unequal-length double-headed studs: suitable for situations where one end is screwed into the body of the component for connection or fastening. See GB897-900, etc.
②Equal-length double-headed studs: suitable for matching the connecting end with the nut to serve as a connection or distance. See GB901, GB953, etc.
⑸ Washers:
① Flat washers: used to overcome the unevenness of the workpiece support surface and increase the stress area of ??the support surface. See GB848, GB95-97 and GB5287.
②Spring (elastic) washers: spring washers see GB93, GB859, etc., elastic washers see GB860, GB955, etc.
③ Anti-return washer: 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, etc.
④ Inclined washers: In order to adapt to the slope of the workpiece support surface, inclined washers can be used. For I-beams, use square bevel washers, see GB852; for channel steel, use square bevel washers, see GB853.
⑹Self-tapping screws:
①Ordinary self-tapping screws: The thread complies with GB5280 (thread for self-tapping screws), with large pitch, suitable for thin steel plates or copper, aluminum, and plastics use. See GB845-847, GB5282-5284, etc.
②Self-tapping locking screws: The threads conform to ordinary metric coarse threads and are suitable for use in situations where vibration resistance is required. See GB6560-6564.
⑺Rivets:
①Hot-forged rivets: Generally larger in size, they are mostly used in locomotives, ships, boilers, etc. The head is usually shaped by hot forging. See GB863-866.
②Cold heading forming rivets: The general diameter specification is ≤16mm, and the head is usually formed by cold heading. See GB867-870, GB109, etc.
③ Hollow and semi-hollow rivets: Hollow rivets, see GB976; semi-hollow rivets, see GB873-875, etc.
④Special purpose rivets: headless rivets, see GB1016; tubular rivets, see GB975; sign rivets, see GB827, etc.
⑤ Blind rivet: It is a single-sided rivet. It is a new type of rivet that has been widely used in recent years. It has the characteristics of speed, safety and convenience, and has the advantages of waterproof and anti-leakage.
⑻ Pin:
① Cylindrical pin: with or without threaded cylindrical pin, see GB119; internally threaded cylindrical pin, see GB120; externally threaded cylindrical pin, see GB878; elastic cylindrical pin, See GB879; cylindrical pin with hole, see GB880, etc.
②Tapered pins: cylindrical pins with or without threads, see GB117; cylindrical pins with internal threads, see GB118; screw-tail tapered pins, see GB881; open-tailed tapered pins, see GB877.
③Cotter pin: Generally matched with screw hole bolts and slotted nuts, it prevents bolts and nuts from loosening. See GB91.
⑼Retaining ring:
①Retaining ring: Use elastic retaining ring with holes. See GB893; elastic retaining rings for shafts. See GB894 and open retaining ring for shaft GB896.
② Steel wire retaining ring: Steel wire retaining ring for holes, see GB895.1; Steel wire retaining ring for shaft, see GB895.2 and steel wire locking ring, see GB921.
③ Locking retaining rings for shafts: retaining rings locked with tapered pins, see GB883; retaining rings locked with screws, see GB884, GB885, etc.
④ Shaft end retaining ring: There are screw-fastened shaft end retaining rings, see GB891 and bolt-fastened shaft end retaining rings, see GB892.
⑽Wood screws:
They are divided into many varieties due to different head shapes and groove types. The head types include round head, countersunk head, semi-countersunk head, etc. The head groove shape is slotted (slotted) and cross slotted. See GB99-101, GB950-952, etc.
3. Mechanical performance levels
⑴Bolts, screws, studs and nuts
Table 1-1: Performance levels of bolts, screws, studs and nuts
⑵Tightening screws
Table 1-2
⑶Self-tapping screws and self-tapping locking screws
Ordinary self-tapping screws It is not classified according to mechanical properties. As long as the appropriate specifications are selected (see GB3098.5 3.6 and Table 3), its general use requirements can be met.
The mechanical performance grade of self-tapping locking screws is divided into two levels: A and B. Grade A is a high-strength grade; Grade B is a low-strength grade.
⑷Stainless steel bolts, screws, studs and nuts
Table 1-3
IV. Accuracy
Standard parts (fastening The accuracy of parts) is determined by the product grade.
Table 1-4: Product grade and accuracy of standard parts (fasteners)
5. Thread
Thread tolerance grade
Standard parts (fasteners) thread tolerance grades
Table 1-5
Note: 1) Only set screws with mechanical properties of 45H and hexagon sockets of grade 12.9 The thread tolerance of screws can be 5g level. (2) Selection of pitch
Comparison of coarse thread and fine thread
Table 1-6
Determine specifications
① For diameter specifications, try to choose the first series of values. Try not to use the values ??in brackets in the product standard size table and try not to use the values ??in the specification table.
②Length specifications generally do not adopt specifications other than those specified in product standards. Generally, when bolts or nuts are matched and connected, it is appropriate for the thread end to be exposed for a length of (0.2-0.3) d.
③ For specifications that match the diameter and length, priority should be given to specifications within the product specification range.