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Bolt, screw, screw three concepts


In life, bolts, screws and screws are often mentioned. What is the difference between them? In fact, the standard saying is there are no screws and nuts. Screw is commonly known, with external thread can be called "screw". The shape of the nut is usually hexagonal, and the inner hole is internal thread, which is used to match the bolt and tighten the relevant parts. Nut is commonly known, the standard should be called "nut". The head of the bolt is usually hexagonal and the rod has an external thread. Screw is small, the head has flat head, cross head, rod with external thread. The studs are actually called "double-headed studs", with external threads at both ends and a smooth rod in the middle. The long end of the thread is used to connect the deep hole, and the short end is used to connect the nut.

Standard fasteners are divided into twelve categories, and the selection of fasteners is determined according to their use occasions and functions.

1, the bolt
Bolts are widely used in mechanical manufacturing for detachable joints, usually with nuts (usually with a washer or two washers).

2, nut

3, screw
The screw is usually used alone (sometimes with a washer), generally fastening or fixing the role, should be screwed into the body of the internal thread.

4, stud
Stud is mainly used to connect one of the connected parts with large thickness, need to use a compact structure or because of frequent disassembly bolt connection is not suitable. Studs are generally threaded at both ends (single-head studs are threaded at the single end), usually a thread firmly screwed into the parts of the body, the other end is matched with the nut, play the role of connection and fastening, but to a large extent also has the role of distance.

5. Wood screws
Wood screws are used for connecting or fastening timber.

6. Tapping screws
The working screw hole matched with the tapping screw does not need to be tapped in advance, and the inner thread is formed when the tapping screw is screwed into the tapping screw.

7, washers
Check washer

The washer is used between the supporting surface of bolts, screws and nuts and the supporting surface of the workpiece to prevent loosening and reduce the stress of the supporting surface.

Lock washer

8, retaining ring

The retaining ring is mainly used to locate, lock or stop the parts on the shaft or in the hole.

Industrial meson

9, pin
Pins are commonly used for positioning, for connecting or locking parts, and as overload shear elements in safety devices.

10, rivets
One end of the rivet has a head and the rod is unthreaded. When used, the rod is inserted into the hole of the connecting piece, and then the end of the rod is riveted and connected or fastened.

11. Connection pair
Coupling is a combination of screw or bolt or tapping screw and washer. After the washer is installed on the screw, it must be free to turn on the screw (or bolt) without falling off. Mainly used for fastening or fastening.

12, other
Mainly including welding nails and other content.

Determine the varieties
(1) The selection principle of varieties
(1) Considering the efficiency of processing and assembly, the varieties of fasteners should be reduced as far as possible in the same machinery or project;
In view of economy, commercial fastener varieties should be preferred.
③ According to the expected requirements of the use of fasteners, according to the type, mechanical properties, accuracy and thread selection, etc.
(2) model
(1) bolt
A) General purpose bolts: there are many varieties, including hexagonal head and square head. Hexagon head bolt application is the most common, according to the manufacturing accuracy and product quality is divided into A, B, C and other product grades, with A and B class application, and mainly used for important, high assembly accuracy and by large impact, vibration or variable load of the place. Hexagonal head bolts can be divided into hexagonal head and large hexagonal head according to the size of the head support area and the size of the installation position; Varieties with holes in the head or screw can be used for locking. The square head of the square head bolt has a large size and force surface, easy to wrench mouth stuck or rely on other parts start and stop action, commonly used in rough structure, sometimes also used in the T-slot, easy to loosen the bolt in the slot to adjust the position. See GB8, GB5780 ~ 5790, etc.
B) Bolts for reaming holes: the bolts should be tightly inserted into the reaming holes to prevent dislocation of the workpiece, as shown in GB27, etc.
C) Check bolts: square neck and tenon, see GB12 ~ 15, etc.;
D) Bolts for special purpose: including T-slot bolts, slotted bolts and anchor bolts. T-slot bolts are used in places where connections are often disassembled; Anchor bolts are used to fix the frame or motor base in cement foundation. See GB798, GB799, etc.
E) High-strength bolt connection pair for steel structure: generally used for friction type connection of steel structure such as building, bridge, tower, pipe support and lifting machinery, see GB3632, etc.
(2) the nut
A) General purpose nuts: there are many kinds of hex nuts, square nuts and so on. Hexagon nut with hexagon bolt is the most common application, according to the manufacturing accuracy and product quality is divided into A, B, C and other product grades. Hexagonal thin nuts are used as secondary nuts in anti-loose devices, for locking, or for threaded joints where shear forces are mainly borne. Hexagon thick nuts are used for frequently disassembled connections. Square nuts and square bolts, spanner stuck not easy to slip, used for rough, simple structure. See GB41, GB6170 ~ 6177, etc.;
B) Slotted nut: mainly refers to the hex slotted nut, that is, the slot is processed above the hex nut. It is used with screw hole bolt and cotter pin to prevent bolt and nut relative rotation, see GB6178 ~ 6181, etc.;
C) Lock nut: refers to nuts with locking function, including nylon insert hex lock nut and full metal hex lock nut, etc. Hexagonal nylon ring lock nut has a very reliable anti-loose ability, in the use of temperature -60 ~ +100℃ and certain medium conditions, with no damage to bolts and connected pieces and can be frequently loaded and unloaded. See GB889, GB6182-6187, etc.
D) Nuts for special purposes: such as butterfly nuts, cover nuts, knurled nuts and insert nuts, etc. Butterfly nut generally can be disassembled without tools, usually used for often dismantled and not much force; Cover nuts are used where the end bolts need to be covered. See GB62, GB63, GB802, GB923, GB806, GB807, GB809, etc.
(3) screw
A) Machine screws: divided into many varieties due to different head and groove shapes. Head type has cylinder head, pan head, countersunk head and half countersunk head a few kinds, head groove shape is to open groove commonly (one word groove), cross groove and inside hexagon groove three kinds. Cross groove screw is good for neutral, head strength is bigger than a word groove, not easy to twist bald, generally used in mass production. Hex socket screw, hex socket flower screw can apply a large tightening torque, the connection strength is large, the head can be embedded in the body, used for compact structure, smooth appearance of the joint. See GB65, GB67-69 and GB818-820, etc.
B) Set screw: set screw is used for the relative position of fixed parts. The head is of the type with a word slot, inner hexagon and square head. The square head can apply a large tightening torque, the top tightening force is large, it is not easy to twist bald, but the head size is large, it is inconvenient to bury in the parts, unsafe, especially the moving parts should not be used. With a word groove, hexagon is easy to sink parts. Set screw end according to the use of different requirements, generally the most commonly used cone end, flat end, cylindrical end three. Conical end is suitable for parts with small hardness; When using non-pointed conical end screws, holes should be made on the top tight surface of the parts, and the conical surface should be pressed on the edge of the holes. Screw for flat end, large contact area, after the top tight does not hurt the surface of parts, used for the top tight hardness of large plane or often adjust the position of the occasion. The cylindrical end screw does not damage the surface of parts, and is mostly used to fix parts mounted on the tube shaft (thin-walled parts). The cylindrical end is pushed into the hole on the shaft, relying on the round end to resist shear action, and can transfer large loads. See GB71, GB73-75, GB77-78, etc.
C) Hex socket screws: hex socket screws are suitable for small installation space or screw head needs to be buried occasions, see GB70, GB6190-6191 and GB2672-2674, etc.;
D) Screws for special purposes: such as positioning screws, non-protruding screws and lifting ring screws, see GB72, GB828-829, GB837-839, GB948-949 and GB825, etc.
(4) stud
A) Unequal length double stud: applicable to the occasions where one end is screwed into the component body for connection or fastening, see GB897-900;
B) Equal-length double-headed stud: suitable for connecting or distance setting with nut at both ends. See GB901, GB953, etc.
5. Wood screw
It is divided into many varieties because of different head and groove shapes. The head type has round head, countersunk head, half countersunk head, head groove for slotted (word groove) and cross groove two kinds, see GB99-101, GB950-952.
⑥ Tapping screw
A) Common tapping screw: thread in line with GB5280, large pitch, suitable for use in thin steel plate or copper, aluminum, plastic, see GB845-847, GB5282-5284, etc.;
B) Tapping locking screw: thread is in line with common metric coarse thread, suitable for vibration resistant occasions, see GB6560 ~ 6564.
All landowners washer
A) Flat washer: used to overcome the uneven supporting surface of the workpiece and increase the stress area of the supporting surface, see GB848, GB95-97 and GB5287;
B) Spring (elastic) washers: spring washers rely on elasticity and diagonal friction to prevent loosening of fasteners, widely used for frequently disassembled connections. The inner tooth elastic washer and the outer tooth elastic washer have a lot of sharp elastic warping teeth on the circumference, and the thorn presses on the support surface to prevent the loosening of fasteners. Inner tooth elastic washer is used under screw head with small head size; Elastic washers with outer teeth are mostly used under bolt heads and nuts. The elastic washer with teeth is smaller than the ordinary spring washer, the fastener has uniform force and is reliable to prevent looseness, but it is not suitable for common disassembly. See GB93, GB859-860 and GB955;
C) Check washers: there are lock washers with inner teeth, lock washers with outer teeth, single-ear stop washers, double-ear stop washers and stop washers for round nuts, etc. Single-ear and double-ear stop washers allow the nut to be tightened at any position to lock, but the fastener should be at the edge of the appropriate, see GB861-862, GB854-855, GB858, etc.;
D) Bevel washer: In order to adapt to the slope of the working support surface, a bevel washer can be used. Square bevel washer is used to pad the inclined surface such as channel steel and I-steel flanges, so that the nut supporting surface is perpendicular to the nail rod, so as to avoid the bending force of the screw when the nut is tightened. See GB852 ~ 853, etc.
End baffle ring
A) Elastic retaining ring: the elastic retaining ring for shaft and hole is clamped in the shaft groove or hole groove for rolling bearings to be loaded and stopped. In addition, there are open retaining rings for shaft, which are mainly used for parts positioning in the shaft groove, but cannot bear axial force. See GB893-894 and GB896;
B) Steel wire retainer: steel wire retainer and steel wire lock ring with holes (for shafts). Steel wire retainer ring installed in shaft groove or hole groove for parts positioning can also bear a certain axial force. See GB895.1 ~.2, GB921;
C) Locking ring for shaft parts: it is used for locking ring with cone pin and locking ring with screw, which is mainly used to prevent axial movement of shaft parts. See GB883-892.
D) Shaft end retainer: the shaft end retainer fastened by screws and the shaft end retainer fastened by bolts are mainly used to lock the parts fixed on the shaft end. See GB883-982.
Pet-name ruby pin
A) Cylindrical pins: cylindrical pins are mainly used for fixing parts on shafts, transferring power, or as positioning components. Cylindrical pins have different diameter tolerances for different mating requirements. The cylindrical pin is usually fixed in the hole by interference, so it is not suitable for more disassembly. See GB119 ~ 120, GB878 ~ 880, etc.
B conical pin: conical pin has a taper of 1:50, easy to install eye, but also to ensure self-locking, generally used for positioning components and connecting components, often used in places requiring frequent disassembly. Tapered and tapered pins with internal thread for holes that do not pass through or in which it is difficult to pin. The end of the tapered pin can be opened after it is driven into the hole to prevent the pin itself from slipping out of the hole. See GB117 ~ 118, GB881 and GB877, etc.
Cylindrical pin and all kinds of conical pin pin hole, generally need to go through ream processing, many times after assembly and disassembly will reduce the accuracy of positioning and connection of fastening, can only transfer small load. Elastic cylinder pin itself has elasticity, installed in the hole to maintain tension, not easy to loose, easy to disassemble, and does not affect the nature of the pin hole does not need to hinge. Pin with hole and pin shaft, both for hinge joints;
C) Split pin: split pin is the anti-loose device connecting the machine parts. When used, it is put into the pin holes of nuts, bolts with pin holes or other connectors, and then the feet are separated. See GB91.
Attending the rivet
A) Hot forging shaped rivet: the general specification is large, and it is mainly used for locomotives, ships and boilers, etc., usually the head is formed by hot forging, see GB863 ~ 866;
B) Cold heading shaped rivet: general diameter specification 16mm, usually by cold heading head molding, see GB867-870, GB109, etc.
C) Hollow and semi-hollow rivets: hollow rivets are used to connect plastic, leather, wood, canvas and other non-metallic parts where shear force is not large.
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