What is the Difference and Function of Bolts and Screws?

What is the Difference Between Screws and Bolts?

Bolts and screws are often mentioned in life. What is the difference between them? Screws are commonly known as screws, and those with external threads can be called screws. The shape of the nut is usually hexagonal, and the inner hole is an inner thread, which is used to cooperate with the bolt and tighten the related parts. The standard of the nut shall be called the nut. The head of the bolt is generally hexagonal, and the shank has external threads. The screw is small, the head has a flat head, a crosshead, etc., and the stem has an external thread. The stud should be called a double-ended stud, with external threads on both ends, and a polished rod in the middle. The long end of the thread is used to connect with the deep hole, and the short end is connected to the nut.

The difference between screws and bolts is not only in appearance, but also in the difference in material and strength. Screws or low-strength bolts are generally made of mild steel wire (SWRM), and are hard extruded into shapes by high-speed impact of a die at room temperature (cold work). High-strength bolts are made of special-purpose alloy steel bolts by forging at high temperature (hot work). The two materials have great strength differences.

What Standard Fasteners are Common to it?

1. A Bolts
   Bolts are widely used in detachable connections in mechanical manufacturing and are generally used in conjunction with nuts (usually plus a washer or two washers).
2. A Nuts
   A nut is a fixing tool with a hole in the center and a spiral thread on the inside of the hole. Nuts are often used with screws of the same size to fix the relevant joints. Nuts are mostly hexagonal, followed by square.
3. A Screws
   Screws are usually used alone, generally for tightening or tightening and should be screwed into the internal thread of the body.
4. A Stud
   Studs are mostly used to connect one of the connected parts with a large thickness and need to be used in places where the structure is compact or the bolt connection is not suitable due to frequent disassembly. Studs are generally threaded at both ends. Usually, one end of the thread is firmly screwed into the body of the component, and the other end is matched with the nut, which plays the role of connection and tightening, to a large extent has the role of distance.
5. A Wood Screws
   Wood screws are used to screw into the wood for connection or fastening.
6. A Self-tapping Screws
   The working screw holes matched with the self-tapping screw do not need to be tapped in advance, and the internal thread is formed at the same time as the self-tapping screw is screwed in.
7. A Washers
   Anti-loose washers are 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.
8. A Retaining Ring
   The retaining ring is mainly used to position, lock, or stop the parts on the shaft or in the hole.
9. A Pin
   Pins are typically used for positioning, but also for connecting or locking parts, and as overload shear elements in safety devices.
10. A Rivets
    The rivet has a head on one end and no thread on the stem. When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is riveted for connection or fastening.
11. A Connection Pair
    The connection pair is a combination of screws or bolts or self-tapping screws and washers. After the washer is installed on the screw, it must be able to rotate freely on the screw (or bolt) without falling off. Mainly play the role of tightening or tightening.

Standard Fastener Type Categories and Their Applications:

1. Types of Bolts
   
   • General purpose bolts: There are many varieties, including hexagonal heads and square heads. Hexagon head bolt applications are mainly used where important, high assembly accuracy and where large shock, vibration, or variable loads are encountered. Hexagon head bolts can be divided into two types: hexagonal head and large hexagonal head according to the size of the head support area and the size of the installation position. There are varieties with holes in the head or screws for use when locking is required. The square head of the square head bolt has a larger size and a force surface, which is convenient for the wrench mouth to be stuck or lean against other parts to prevent rotation.
   • Bolts for reaming holes: When in use, the bolts are tightly inserted into the reaming holes to prevent the dislocation of the workpiece.
   • Anti-rotation bolt: There are square neck and tenon.
   • Special-purpose bolts: Including T-slot bolts, joint bolts, and anchor bolts. T-slot bolts are mostly used in places that need to be disconnected frequently. Anchor bolts are used to fix the frame or motor base in the cement foundation.
   • High-strength bolt connection pair for steel structure: Generally used for friction-type connection of steel structures such as buildings, bridges, towers, pipeline supports, and hoisting machinery.
2. Types of Nuts
   
   • General purpose nuts: There are hexagonal nuts, square nuts, etc. Hex nuts are most used with hex bolts. Hexagonal thin nuts are used as auxiliary nuts in anti-loosening devices, which play a locking role or are used in places where the threaded connection pair is mainly subjected to shearing force. Hexagonal thick nuts are used in connections that are frequently disassembled. The square nut is matched with the square head bolt, and the wrench is not easy to slip, and it is used for rough and simple structures.
   • Slotted nut: Refers to the hexagonal slotted nut, that is, a groove is machined above the hexagonal nut. It is used in conjunction with threaded hole bolts and cotter pins to prevent relative rotation of the bolt and nut.
   • Locknut: Refers to the nut with locking function, including nylon insert hexagonal lock nut and all-metal hexagonal lock nut. The hexagonal nylon ring lock nut has a very reliable anti-loosening ability. Under the operating temperature of -60 ~ +100 ℃ and certain medium conditions, it has no damage to the bolt and the connected parts and can be frequently loaded and unloaded.
   • Nuts for special purposes: Such as wing nuts, cap nuts, knurled nuts and insert nuts, etc. Wingnuts can generally be disassembled and assembled without tools, and are usually used in places that need to be disassembled frequently and are not subject to much force. Cap nuts are used where end caps are required.
3. Types of Screw
   
   • Machine screws: They are divided into many varieties due to different head shapes and groove shapes. There are three types of head types: cylindrical head, pan head, countersunk head, and semi-sink head. The cross recessed screw has good neutrality when screwing, and the head strength is larger than that of the slotted one, and it is not easy to be bald. It is generally used in mass production. Hexagon socket head cap screws and socket head cap screws can apply a large tightening torque, have high connection strength, and the head can be embedded in the body.
   • Set screws: Set screws are used to fix the relative position of the parts, and the head has the type with slot, socket angle and square head. The square head can apply a large tightening torque, and the top tightening force is large, and it is not easy to be screwed. Slotted and hexagonal for easy sinking of parts. The end of the set screw is different according to the requirements of use, and the most used ones are tapered end, flat end, and cylindrical end. The taper end is suitable for parts with low hardness; when using a pointless taper end screw, a hole should be punched on the top surface of the part, and the taper surface should be pressed against the edge of the hole. The screw with the flat end at the end has a large contact area and does not damage the surface of the part after being tightened. The screw with the cylindrical end does not damage the surface of the part, and is mostly used to fix the parts mounted on the pipe shaft. The cylindrical end is pushed into the hole on the shaft, and the shear resistance of the round end can transmit a large load.
   • Hexagon socket head cap screws: The socket head cap screws are suitable for occasions where the installation space is small or the screw head needs to be embedded.
   • Screws for special purposes: Such as positioning screws, non-prolapse screws, and eye screws.
4. Types of Studs
   
   • Unequal length studs: Suitable for occasions where one end is screwed into the body of the component for connection or fastening.
   • Equal length stud: Suitable for matching with nuts at both ends for connection or distance.
5. Types of Wood Screws
   Divided into many varieties due to different head shapes and groove shapes. There are several types of heads, such as round heads, countersunk heads, and semi-sink heads.
6. Type of Self-tapping Screw
   
   • Ordinary self-tapping screws: A large pitch, suitable for use on thin steel plates or copper, aluminum, and plastic.
   • Self-tapping locking screw: The thread conforms to ordinary metric coarse thread, which is suitable for use in applications requiring vibration resistance.
7. Types of Gaskets
   
   • Flat washer: Used to overcome the unevenness of the support surface of the workpiece and increase the stress area of the support surface.
   • Spring washers: Spring washers rely on elasticity and oblique friction to prevent the loosening of fasteners, and are widely used infrequently disassembled connections. The inner tooth elastic washer and the outer tooth elastic washer have many sharp elastic warping teeth on the circumference, which are pressed against the supporting surface and can prevent the loosening of the fastener. The inner tooth elastic washer is used under the screw head with a smaller head size; the outer tooth elastic washer is mostly used under the bolt head and the nut. The elastic washer with teeth is smaller than the ordinary spring washer, and the fastener is evenly stressed and reliable to prevent loosening, but it is not suitable for frequent disassembly.
   • Backstop washers: There are internal tooth lock washers, external tooth lock washers, single-ear stop washers, double-ear stop washers, stop washers for round nuts, etc. Single and double lug lock washers allow the nut to be tightened in any position to lock, but fasteners need to be close to the edge.
   • Oblique washer: To adapt to the inclination of the working bearing surface, an oblique washer can be used. Square inclined washers are used to flatten the inclined surfaces such as channel steel and I-beam flanges, so that the bearing surface of the nut is perpendicular to the nail rod, to avoid the bending force of the screw rod when the nut is tightened.
8. Type of Retaining Ring
   
   • Retaining ring: The elastic retaining ring for shaft and hole is clamped in the shaft groove or hole groove for the rolling bearing to be installed and back-stopped. In addition, there is an open retaining ring for the shaft, which is mainly used to be clamped in the shaft groove as a part It is used for positioning, but cannot bear axial force.
   • Wire retaining ring: Wire retaining ring and wire locking ring with holes (for shaft). The steel wire retaining ring can also bear a certain axial force when it is installed in the shaft groove or hole groove for part positioning.
   • Locking retaining rings for shaft parts: Retaining rings locked with taper pins and retaining rings locked with screws are mainly used to prevent the axial movement of parts on the shaft.
   • Shaft end retaining ring: The shaft end retaining ring fastened with screws and the shaft end retaining ring fastened with bolts are mainly used to lock the parts fixed on the shaft end.
9. Types of Pins
   
   • Cylindrical pins: Cylindrical pins are mostly used to fix parts on the shaft, transmit power, or act as positioning elements. Cylindrical pins have different diameter tolerances for different fit requirements. Cylindrical pins are generally fixed in the holes by interference, so they should not be disassembled.
   • Tapered pin: The tapered pin has a taper of 1:50, which is easy to install on the eye and can ensure self-locking. It is generally used as a positioning element and a connecting element and is mostly used in places that require frequent disassembly. Internally threaded taper pins and threaded tail taper pins for use in holes that do not pass through or in holes where it is difficult to drive a pin. The end of the split tapered pin can be opened after being driven into the hole, preventing the pin itself from slipping out of the hole. The pinholes of cylindrical pins and various tapered pins generally need to be reamed. After repeated assembly and disassembly, the positioning accuracy and connection tightening will be reduced, and only a small load can be transmitted. The elastic cylindrical pin itself is elastic, and it is installed in the hole to maintain tension, it is not easy to loosen, it is easy to disassemble, and does not affect the matching property, and the pinhole does not need to be hinged.
   • Cotter pin: Cotter pin is an anti-loosening device for connecting parts. When in use, it is inserted into nuts, bolts with pinholes of other connectors, and then the feet are separated.
10. Types of Rivets
    
    • Hot forging rivets: Generally larger, mostly used in locomotives, ships, and boilers, etc. Usually, the head needs to be formed by hot forging.
    • Cold heading rivets: The general diameter is 16mm, and the head is usually formed by cold heading.
    • Hollow and semi-hollow rivets: Hollow rivets are used in places with little shear force and are often used to connect non-metallic parts such as plastics, leather, wood, and canvas.