Fasteners are widely used and are usually called standard parts in the market. Fasteners are not only diversified but also in great demand. In the process of use, we need to select appropriate types to fasten and connect mechanical parts according to the specific actual situation. Next, Xiaorui will lead you to understand the selection principles of fasteners.
Selection principle of fasteners
1、 Determine category
The standard fasteners are divided into ten categories, and the selection shall be determined according to the use occasions and functions of the standard fasteners.
① Bolt: the bolt is generally matched with the nut (usually with one washer or two washers) for connection and fastening purposes.
② Nuts: nuts are used together with bolts.
③ Screws: Screws are usually used separately (sometimes with washers), generally for fastening or tightening.
④ Stud: Generally, both ends of the stud are threaded (single end stud is threaded at one end). Usually, one end of the stud is firmly screwed into the component body, and the other end is matched with the nut for connection and fastening, but to a large extent, it also has the function of spacing.
⑤ Washer: the washer is used between the bearing surface of bolts, screws and nuts and the process bearing surface to prevent looseness and reduce the stress on the bearing surface.
⑥ Self tapping screw: the screw hole of the workpiece matched with the self tapping screw does not need to be tapped in advance, and the internal thread is formed when the self tapping screw is screwed in.
⑦ Rivet: one end of the rivet has a head and the rod has no thread. When in use, insert the rod into the hole of the connected part, and then rivet the end of the rod tightly for connection or fastening.
⑧ Pin: The pin is inserted into the workpiece during use, and usually plays the role of connection or positioning.
⑨ Retaining ring: The retaining ring is usually on the shaft or in the hole, which limits the axial direction of the workpiece.
⑩ Wood screw: wood screw is used to screw into wood for connection or fastening.
2、 Determine standards and varieties
1. Selection principle of varieties:
⑴ Considering the working efficiency of processing and assembly, the variety of standard parts shall be minimized in the same machinery or project.
(2) In consideration of economy, the standard commodity parts shall be selected preferentially.
(3) According to the expected use requirements of standard parts, the type, mechanical performance, accuracy and thread shall be selected.
2. Type:
⑴ Bolts:
① General purpose bolts: there are many varieties, including hexagonal head and square head. See national standard GB5780-GB5790, etc.
② Bolt for reaming: the bolt shall be closely inserted into the reamed hole during use to prevent dislocation of the workpiece, see GB27, etc.
③ Stop bolt: it can be divided into square neck and belt neck, see GB12-15, etc.
④ Special purpose bolts: see GB37 for T-slot bolts; Movable joint bolt, see GB798; For anchor bolts, see GB799, etc.
⑤ High strength bolt connection pairs for steel structures: generally used for friction type connection of steel structures such as buildings, bridges, towers, pipe supports and hoisting machinery, see GB3632, etc.
⑵ Nut:
① Nuts for general purposes: mainly refer to hexagonal nuts, and square nuts, with many varieties, see GB41, GB6170-6177, etc.
② Slotted nut: mainly refers to the hexagon slotted nut, that is, the groove is processed above the hexagon nut. It is used together with threaded bolt with hole and cotter pin to prevent the relative rotation of bolt and nut. See GB6178-6181, etc.
③ Lock nut: refers to the nut with locking function, including nylon insert hexagon lock nut, see GB889, GB6182, GB6183 and all metal hexagon lock nut, see GB6184-6187.
④ Special purpose nuts: such as dished nuts, see GB62; Ring nut, see GB63; See GB802 and GB923 for cap nuts; Knurled nuts, see GB806, GB807 and embedded nuts, see GB809, etc.
(3) Screw:
① Machine screws: They are divided into many varieties due to different head type and groove type. The head type includes cylindrical head, pan head, countersunk head and semi countersunk head, and the head type includes slotted (straight metal) and cross groove. See GB65, GB67-69, GB818-820, etc.
② Set screw: the set screw uses its tail end to prevent mutual displacement between workpieces and transfer less torque. See GB71, GB73-75, GB77, GB78, etc.
③ Socket head cap screws: Socket head cap screws are suitable for situations where the installation space is small or the screw head needs to be embedded., See GB70, GB6190, GB6191 and GB2672-2674.
④ Special purpose screws: such as set screws, see GB72, GB828 and GB829; See GB827-839, GB948, GB948 and eyebolts, GB825, etc.
(4) Stud:
① Unequal length double head stud: applicable to the occasion where one end is screwed into the body of the component for connection or fastening. See GB897-900, etc.
② Equal length double head stud: suitable for matching the connecting end with the nut for connection or spacing. See GB901, GB953, etc.
(5) Washer:
① Flat washer: used to overcome the unevenness of the workpiece bearing surface and increase the stress area of the bearing surface. See GB848, GB95-97 and GB5287.
② Spring (elastic) washer: see GB93, GB859, etc. for spring washer, and GB860, GB955, etc. for elastic washer.
③ Back washer: lock washer with internal teeth, see GB861; External tooth lock washer, see GB862; Single lug tab washer, see GB854; Double lug tab washer, see GB855; Round nut lock washer, see GB858, etc.
④ Bevel washer: To adapt to the slope of the workpiece supporting surface, bevel washer can be used. Square bevel washer is used for I-shaped steel, see GB852; See GB853 for square bevel washer used for channel steel.
(6) Self tapping screw:
① Ordinary self tapping screw: the thread shall conform to GB5280 (thread for self tapping screw), and the thread pitch is large, which is suitable for use on thin steel plate or copper, aluminum and plastic. See GB845-847, GB5282-5284, etc.
② Self tapping locking screw: The thread conforms to the common metric coarse thread, and is suitable for use in the occasion where vibration resistance is required. See GB6560-6564.
(7) Rivets:
① Hot forged rivet: Generally, it is large in size and is mainly used for locomotives, ships and boilers. It is usually necessary to shape the head by hot forging. See GB863-866.
② Cold heading rivet: the diameter specification is generally ≤ 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; For semi hollow rivets, see GB873-875, etc.
④ Rivets for special purposes: with or without head, see GB1016; Tubular rivet, see GB975; See GB827, etc. for nameplate rivets.
⑤ Blind rivet: It is a kind of rivet with single side riveting. It is a new type of rivet widely used in recent years. It is fast, safe, convenient and has the advantages of waterproof and anti leakage.
(8) Pin:
① Cylindrical pin: with or without thread, see GB119; Internal thread cylindrical pin, see GB120; External thread cylindrical pin, see GB878; Elastic cylindrical pin, see GB879; Cylindrical pin with hole, see GB880, etc.
② Taper pin: with or without threaded cylindrical pin, see GB117; Internal thread cylindrical pin, see GB118; Taper pin with screw tail, see GB881; Split taper pin, see GB877.
③ Cotter pin: It is generally matched with threaded bolt with hole and slotted nut to prevent the bolt and nut from loosening. See GB91.
(9) Retaining ring:
① Circlip: Circlip with holes. See GB893; Circlip for shaft. See GB894 and GB896 for shaft split ring.
② Steel wire retainer ring: steel wire retainer ring with holes, see GB895.1; See GB895.2 and GB921 for steel wire retainer ring for shaft.
③ Locking retaining ring for shaft parts: see GB883 for retaining ring locked with taper pin; See GB884, GB885, etc. for retaining rings locked with screws.
④ Shaft end retainer ring: see GB891 for shaft end retainer ring fastened with screws and GB892 for shaft end retainer ring fastened with bolts.
(10) Wood screw:
It is divided into many varieties due to different head type and groove type. The head type includes round head, countersunk head, semi countersunk head, etc. The head groove type includes slotted (slot) and cross groove. See GB99-101, GB950-952, etc.
3、 Mechanical property grade
⑴ Bolts, screws, studs and nuts
Table 1: Performance grades of bolts, screws, studs and nuts
(2) Set screw
Table 2
(3) Self tapping screws and self tapping locking screws
Ordinary self tapping screws are not graded according to their mechanical properties. As long as appropriate specifications are selected, see Article 3.6 and Table 3 of GB3098.5 for general requirements.
The mechanical properties of self tapping locking screws are divided into two grades: A and B. Grade A is high strength grade; Grade B is low strength grade.
(4) Stainless steel bolts, screws, studs and nuts
Table 3
4、 Precision
The accuracy of standard parts (fasteners) is determined by the product grade.
Table 4: Product Grade and Accuracy of Standard Parts (Fasteners)
5、 Thread
Thread tolerance class
Table 5 Thread Tolerance Grades of Standard Parts (Fasteners)
Note: 1) Only the thread tolerance of set screws with mechanical properties of 45H and socket head cap screws with mechanical properties of 12.9 can be Grade 5g. (2) Selection of pitch.
Table 6 Comparison between coarse thread and fine thread
Determine specifications
① The first series of values shall be selected as far as possible for the diameter specification, and the values in brackets in the product standard dimension table and the values in the specification table shall not be used as far as possible.
② Generally, the length specification does not apply the specification beyond the product standard. In general, when bolts or nuts are matched, it is appropriate to expose (0.2-0.3) d at the end of the thread.
③ For the specifications matching the diameter and length, the specifications within the range of commodity specifications shall be preferred.
For Jinrui, whether you are a fastener demander/dealer/supplier, you can visit the official website of Jinrui for more information: https://www.jinruibolt.com/
