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Differences Among Bolts, Screws And Bolts(一)

Feb 23, 2019

Differences among Bolts, Screws and Bolts

(1) Selection Principles of Varieties

Considering the efficiency of processing and assembling, the variety of fasteners should be minimized in the same machinery or engineering.

(2) For economic consideration, commodity fasteners should be selected first.

(3) According to the anticipated usage requirements of fasteners, the types of fasteners should be selected according to their types, mechanical properties, accuracy and threads.

(2) type


A) General purpose bolts: There are many kinds of bolts, which can be divided into hexagonal head and square head. Hexagonal head bolts are most commonly used. According to manufacturing accuracy and product quality, they are classified into A, B, C and other product grades. A and B are the most widely used. They are mainly used in important, high assembly accuracy and places subject to greater impact, vibration or variable load. Hexagonal head bolts can be divided into hexagonal head and large hexagonal head according to the size of support area and installation position of the head. Varieties with holes in the head or screw can be used when locking is needed. The square head bolt has larger size and stress surface, which is easy for wrench to clamp or rely on other parts to stop rotation. It is often used in rough structure and sometimes in T-groove, so that the bolt can be loosened and adjusted in the groove. See GB8, GB5780-5790, etc.

B) Bolts for articulated holes: When used, the bolts are tightly inserted into the articulated holes to prevent dislocation of the workpiece. See GB27, etc.

C) Rotary stop bolts: with square neck and tenon, see GB12-15, etc.

D) Special purpose bolts: including T-groove bolts, movable bolts and anchor bolts. T-groove bolts are mostly used in places where connection needs to be frequently dismantled; foot bolts are used to fix frame or motor base in cement foundation. See GB798, GB799, etc.

E) High-strength bolt connection pairs for steel structures: commonly used in friction connection occasions of steel structures such as buildings, bridges, towers, pipeline brackets and lifting machinery, see GB3632, etc.


A) General purpose nuts: There are many kinds of nuts, such as hexagonal nuts, square nuts, etc. Hexagonal nuts with hexagonal bolts are most commonly used. According to manufacturing accuracy and product quality, hexagonal nuts are classified into grade A, B and C. Hexagonal thin nuts are used as auxiliary nuts in anti-loosening devices to lock or where the thread connection vice bears shear stress. Hexagonal thick nuts are mostly used in connection which is often disassembled. Square nut with square head bolt, wrench clamping is not easy to slip, mostly used for rough and simple structure. See GB41, GB6170-6177, etc.

B) Slotted nuts: mainly refers to hexagonal slotted nuts, that is, the processing of slots above the hexagonal nuts. It is used in conjunction with bolts with holes and opening pins to prevent the relative rotation of bolts and nuts. See GB6178-6181, etc.

C) Locking nuts: refers to nuts with locking function, such as nylon insert hexagonal locking nuts and all-metal hexagonal locking nuts. Hexagonal nylon ring locking nut has a very reliable anti-loosening ability. Under the conditions of using temperature - 60 ~100 ~C and certain medium, it has some advantages, such as no damage to bolts and connectors, frequent loading and unloading, etc. See GB889, GB6182-6187, etc.

D) Special purpose nuts: such as butterfly nuts, cover nuts, knurling nuts and embedded nuts. Butterfly nuts can be disassembled and assembled without tools. They are usually used in places where they are often disassembled and under little stress. Cover nuts are used in places where end bolts need cover. See GB62, GB63, GB802, GB923, GB806, GB807, GB809, etc.


A) Machine screw: It is divided into many varieties according to the head type and groove shape. Head type has cylindrical head, disk head, countersunk head and semi-countersunk head. Head groove is generally grooved (one-word groove), cross groove and inner hexagonal groove. The cross groove screw has good alignment when it is twisted. The head strength is larger than that of the single groove, and it is not easy to screw bald. It is usually used in mass production. The inner hexagonal screw and the inner hexagonal flower screw can exert greater tightening moment, and have strong connection strength. The head can be embedded in the body, which is used for the connection where the structure is compact and the shape is smooth. See GB65, GB67-69 and GB818-820, etc.

B) Fixed screw: Fixed screw is used to fix the relative position of parts, head with a slot, hexagonal and square head type. Square head can exert a larger tightening moment, the tightening force is large, and it is not easy to screw bald, but the size of the head is large, it is not safe to bury in parts, especially in moving parts. With a slot, the inner hexagonal is easy to sink parts. According to the different requirements of use, the most commonly used tightening screw ends are cone end, flat end and cylindrical end. Cone end is suitable for parts with small hardness; when using non-pointed cone end screw, holes should be made on the top surface of the parts, and the cone face is pressed on the edge of the holes. The screw with flat end has large contact area and does not damage the surface of the parts after tightening. It is used to tighten the plane with high hardness or to adjust the position frequently. The screw at the end of the cylinder does not damage the surface of the parts. It is mostly used to fix the parts mounted on the tube shaft (thin-walled parts). The holes at the end of the cylinder top into the shaft can transmit larger loads depending on the shear resistance of the end of the cylinder. See GB71, GB73-75, GB77-78, etc.

If you want to see the following details, please see the next breakdown.