I. Determine the category
Standard fasteners are divided into ten categories. When selecting a standard fastener, the choice should be based on the application and function of the fastener.
① Bolts: Bolts are generally used with nuts (usually with one or two washers) for connection and fastening.
② Nuts: Nuts are used in conjunction with bolts.
③ Screws: Screws are usually used alone (sometimes with washers) and are generally used for fastening or securing.
④ Studs: Studs are generally threaded at both ends (single-ended studs are threaded at only one end). Usually, one end is firmly screwed into the component body, and the other end is matched with a nut, which serves to connect and fasten, but also plays a significant role in spacing.
⑤ Washers: Washers are used between the bearing surface of bolts, screws, and nuts and the process bearing surface to prevent loosening and reduce the stress on the bearing surface.
⑥ Self-tapping screws: The workpiece screw hole that is matched with the self-tapping screw does not need to be pre-tapping. The internal thread is formed when the self-tapping screw is screwed in.
⑦ Rivet: A rivet has a head at one end and no threads on the shank. When used, the shank is inserted into the hole of the part being connected, and then the end of the shank is riveted to connect or fasten it.
⑧ Pin: When in use, a pin is inserted into the workpiece and usually serves to connect or position it.
⑨ Retaining ring: Retaining rings are usually on the shaft or inside the hole, and serve to restrict the axial direction of the workpiece.
⑩ Wood screws: Wood screws are used to screw into wood for connection or fastening.
II. Determining Standards and Varieties
1. Principles for variety selection:
(1) Considering the efficiency of processing and assembly, the variety of standard parts used should be minimized within the same machine or project.
(2) From an economic perspective, standard parts should be given priority.
(3) Based on the expected usage requirements of standard parts, determine the selection of types according to their type, mechanical properties, precision and thread.
2. Type:
(1) Bolt:
① General purpose bolts: There are many varieties, including hexagonal head and square head bolts, see national standards GB5780-GB5790, etc.
② Bolts for reamed holes: When using them, the bolts are tightly inserted into the reamed holes to prevent workpiece misalignment, see GB27, etc.
③ Anti-rotation bolts: There are square neck and tapered types, see GB12-15, etc.
④ Special purpose bolts: such as T-slot bolts, see GB37; hinge bolts, see GB798; anchor bolts, see GB799, etc.
⑤ High-strength bolted connections for steel structures: These are generally used for friction-type connections in steel structures such as buildings, bridges, towers, pipe supports, and lifting machinery, see GB3632, etc.
(2) Nut:
① General purpose nuts: mainly refers to hexagonal nuts, and there are also square nuts. There are many varieties, see GB41, GB6170-6177, etc.
② Slotted nuts: These mainly refer to hexagonal slotted nuts, which have slots machined into the top of the hexagonal nut. They are used in conjunction with bolts with holes and cotter pins to prevent relative rotation between the bolt and nut, see GB6178—6181, etc.
③ Locking nuts: These are nuts with locking functions. There are hexagonal locking nuts with nylon inserts, see GB889, GB6182, GB6183, and all-metal hexagonal locking nuts, see GB6184-6187.
④ Special purpose nuts: such as disc nuts, see GB62; ring nuts, see GB63; cap nuts, see GB802 and GB923; knurled nuts, see GB806 and GB807; and embedded nuts, see GB809, etc.
(3) Screws:
① Machine screws: Divided into many varieties due to differences in head shape and slot shape. Head shapes include cylindrical head, pan head, countersunk head, and semi-countersunk head. Head shapes are available in slotted (slotted) and Phillips head. See GB65, GB67-69, and GB818-820, etc.
② Set screw: The set screw uses its tail end to prevent displacement between workpieces and to transmit a small amount of torque. See GB71, GB73-75, GB77, GB78, etc.
③ Hex socket head cap screws: Hex socket head cap screws are suitable for applications with limited installation space or where the screw head needs to be recessed. See GB70, GB6190, GB6191 and GB2672-2674, etc.
④ Special purpose screws: such as positioning screws, see GB72, GB828, GB829; non-removable screws, see GB827-839, GB948, GB948 and eye bolts, see GB825, etc.
(4) Studs:
① Unequal-length double-ended studs: Suitable for applications where one end is screwed into the component body for connection or fastening. See GB897-900, etc.
② Equal-length double-ended studs: Suitable for use with nuts at the connecting end, serving as a connector or for spacing. See GB901, GB953, etc.
(5) Washers:
① Flat washers: Used to overcome unevenness of the workpiece support surface and increase the stress area of the support surface. See GB848, GB95-97 and GB5287.
② Spring (elastic) washers: Spring washers are found in GB93, GB859, etc., and elastic washers are found in GB860, GB955, etc.
③ Locking washers: There are internal tooth locking washers, see GB861; external tooth locking washers, see GB862; single-ear locking washers, see GB854; double-ear locking washers, see GB855; round nut locking washers, see GB858, etc.
④ Angled washers: Angled washers can be used to accommodate the slope of the workpiece's supporting surface. Square angled washers are used for I-beams (see GB852); square angled washers are used for channel steel (see GB853).
(6) Self-tapping screws:
① Ordinary self-tapping screws: The thread conforms to GB5280 (threads for self-tapping screws), with a large pitch, suitable for use on thin steel plates or copper, aluminum, and plastics. See GB845—847, GB5282—5284, etc.
② Self-tapping locking screws: The threads conform to ordinary metric coarse threads, suitable for use in applications requiring vibration resistance. See GB6560—6564.
(7) Rivets:
① Hot-forged rivets: These are generally larger in size and are mostly used in locomotives, ships, and boilers. They usually require hot forging to shape the head. See GB863-866.
② Cold-forged rivets: Generally, the diameter is ≤16mm, and the head is usually formed by cold forging. See GB867-870, GB109, etc.
③ Hollow and semi-hollow rivets: Hollow rivets, see GB976; Semi-hollow rivets, see GB873-875, etc.
④ Special purpose rivets: Headless rivets (see GB1016); tubular rivets (see GB975); nameplate rivets (see GB827), etc.
⑤ Blind rivets: These are single-sided riveting rivets and are a new type of rivet that has been widely used in recent years. They are quick, safe, and convenient, and also have the advantages of being waterproof and leak-proof.
(8) Sales:
① Cylindrical pins: threaded cylindrical pins, see GB119; internally threaded cylindrical pins, see GB120; externally threaded cylindrical pins, see GB878; flexible cylindrical pins, see GB879; cylindrical pins with holes, see GB880, etc.
② Tapered pins: threaded cylindrical pins, see GB117; internally threaded cylindrical pins, see GB118; threaded tapered pins, see GB881; open-ended tapered pins, see GB877.
③ Cotter pin: Generally used with bolts with holes and slotted nuts to prevent bolts and nuts from loosening. See GB91.
(9) Stop ring:
① Elastic retaining rings: Elastic retaining rings with holes. See GB893; elastic retaining rings for shafts. See GB894 and GB896 for open retaining rings for shafts.
② Wire retaining rings: Wire retaining rings with holes, see GB895.1; Wire retaining rings for shafts, see GB895.2; and Wire locking rings, see GB921.
③ Locking rings for shaft components: There are retaining rings that are locked with tapered pins, see GB883; and retaining rings that are locked with screws, see GB884, GB885, etc.
④ Shaft end retaining ring: Shaft end retaining rings fastened with screws, see GB891 and shaft end retaining rings fastened with bolts, see GB892.
(10) Wood screws:
Different varieties are made from different head and groove shapes. Head shapes include round head, countersunk head, and semi-countersunk head, while groove shapes include slotted (straight groove) and cross-shaped groove. See GB99-101, GB950-952, etc.
III. Mechanical Performance Grade
(1) Bolts, screws, studs and nuts
Table 1-1: Performance Grades of Bolts, Screws, Studs and Nuts
performance
grade
Nut
4
5
6
8
9
10
12
bolt
screw
Stud
3.6,
4.6
4.8
5.6
5.8
6.8
8.8
9.8
10.9
12.9
Applicable
occasion
Low strength, low torque
High strength, high torque
(2) Set screw
Table 1-2
performance level
14H
22H
33H
45H
Applicable occasions
Low strength, low torque
High strength, high torque
(3) Self-tapping screws and self-tapping locking screws
Ordinary self-tapping screws are not classified according to mechanical properties. As long as the appropriate size is selected (see Clause 3.6 and Table 3 in GB3098.5), their general usage requirements can be met.
Self-tapping locking screws are classified into two mechanical property grades: A and B. Grade A represents high strength, while Grade B represents low strength.
(4) Stainless steel bolts, screws, studs and nuts
Table 1-3
Material Category
performance level
Austenitic
——
A1-50
A2-50
A3-50
——
A1—70
A2-70
A3-70
A1—80
A2—80
A3-80
C martensite
——
C1—50
C4-50
——
C1—70
C4-70
C3-80
F ferrite
F1-45
——
F1-60
——
——
Applicable occasions
Low strength, low torque
High strength, high torque
IV. Accuracy
The precision of standard parts (fasteners) is determined by the product grade.
Table 1-4: Product Grades and Precision Levels of Standard Parts (Fasteners)
Part
Product Grade
A
B
C
Threads, rod and bearing surface
Tight
Tight
pine
Other parts
Tight
pine
pine
Accuracy
accurate
More accurate
Inaccurate
V. Threads
Thread tolerance grade
Standard parts (fasteners) thread tolerance grades
Table 1-5
Thread tolerance grade
Corresponding product grade
Applicable occasions
internal thread
6H
A, B
Threads are used in general machinery and tools.
external thread
5g1
6g
internal thread
7H
C
Ribbed seams are used in construction and other environments with poor working conditions.
external thread
8g
Note: 1) Only set screws with mechanical properties of grade 45H and socket head cap screws with grade 12.9 can use a thread tolerance of grade 5g. (2) Selection of thread pitch
Comparison of coarse and fine threads
Table 1-6
coarse thread
Fine thread
It has good versatility and economy, is suitable for rapid fastening operations, and is suitable for repeated loading and unloading.
It has good anti-loosening properties and high fastening force and strength.
Determine specifications
① When choosing diameter specifications, try to select values from the first series and avoid using values in parentheses in the product standard size table or values from other specification tables.
② The length specification should generally not be other than the specifications stipulated in the product standard. When bolts or nuts are connected, the length of the thread end that protrudes is generally (0.2-0.3)d.
③ For specifications that match the diameter and length, those within the range of product specifications should be selected first.
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