What is the Difference and Function of Bolts and Screws?

What is the Difference Between Screws and Bolts?

Bolts and screws are commonly used every day for fastening. Screws are usually tapered and create their own thread in the material they are turned into. Screws are usually small and can have a head that is flat or rounded. The head can have either a plus shaped slot for screwing or a straight slot. A bolt is not tapered and often uses a washer along with a nut which is screwed onto the end of the bold after it is passed though holes in the material to be held together. The head of the bolt is generally hexagonal, and the shank has external threads. The shape of the nut is usually hexagonal, and the inner hole has an inner thread which matches the thread on the bolt so it can be screwed on and tightened.

Bolds and screws also differ in strength according to the material they are made with. 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.

Common Standard Fasteners:

1. Bolts
   Bolts are widely used in detachable connections in mechanical manufacturing and are generally used in conjunction with nuts (usually along with one or two washers).
2. 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 used with screws of a size matching the bolt. Nuts are usually hexagonal but square nuts are also used.
3. Screws
   Screws are usually used alone and are screwed into the body of the material to be fastened.
4. Studs
   Studs are like bolts but are generally threaded at both ends. They are usually used to connect large objects where the structure is not suitable for frequent disassembly. One end of the thread is firmly screwed into the body of the component, and the other end is matched with a nut, which is tightened to make the connection.
5. Wood Screws
   Wood screws are a type of self-tapping screw used to screw into wood for connecting or fastening.
6. Self-tapping Screws
   Self-tapping screws a do not need to be tapped in advance. As the self-tapping screw is screwed in, it forms an internal thread in the material it is being screwed into.
7. Washers
   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 on the supporting surface.
8. Retaining Rings
   TRetaining rings are metal fasteners that are inserted into a slot on the shaft of an apparatus to retain a part onto the shaft.
9. Pins
   Pins are typically used for positioning an assembly while connecting with other connectors. Shear pins are also used as an overload safety devices that will shear off if an excessive force is applied.
10. Rivets
    Rivet have a head on one end and no thread on the narrow end called the tail. The tail is inserted into the holes of the pieces to be connected, and then the end of the tail is hammered to flatten it for connecting or fastening.
11. Connection Pairs
    The connection pair is a combination of screws, bolts, or self-tapping screws with washers. After the washer is installed on the screw, it must be able to rotate freely on the screw (or bolt) without falling off. Its main purpose is for ease of tightening and adding support to the material being fastened.

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. A square head bolt has a larger size and can take a larger torque force when being tightened. This can prevent the wrench mouth from slipping while tightening.
   • Bolts for reaming holes: Bolts that fit tightly in the hole they are inserted into to prevent dislocation of the workpiece.
   • Anti-rotation bolts: Bolts with a square neck on the shank just below the head that prevents rotation of the bolt when the nut is being tightned.
   • Special-purpose bolts: T-slot bolts are used in places that need to be disconnected frequently. Anchor bolts are used to fix the frame of a structure or a motor base to a cement foundation.
   • High-strength bolt connection pairs for steel structures: 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: Hexagonal nuts are usually used along with hexagonal bolts for connections that are frequently disassembled. Square nuts are less prone to having the wrench slip and are usually used along with square head bolts for rough or simple structures.
   • Slotted nuts: Hexagonal slotted nuts have a groove machined across the hexagonal nut and are used in conjunction with threaded hole bolts and cotter pins to prevent rotation of the nut on the bolt.
   • Locknuts: Nuts with a locking function. Hexagonal nylon ring lock nuts have a very reliable anti-loosening property.
   • Nuts for special purposes: Wingnuts can generally be disassembled and assembled without tools, and are usually used in places that need to be disassembled frequently and require little force to tighten or loosen. Cap nuts are used where end caps are required to protect the nut, or the materials they are attached to.
3. Types of Screw
   
   • Machine screws: Screws can have a variety of different head shapes and groove shapes. There are four common head types:
     • Cylindrical head screws have a small head diameter and can be countersunk easily into wood.
     • Pan head screws have wide heads and a flat, slightly domed bearing top surface with a recessed socket. They are typically used for wood.
     • Counter-sink screws, also known as a “flat-head screws,” sink into a surface and rest flush in the material.
     • Set screws are used to fix the relative position of parts. The screw head has a large flat contact area and does not damage the surface of the part after being tightened.
     • Hexagon socket head cap screws are suitable where the installation space is small or the screw head needs to be embedded.
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
   Wood screws can have different head shapes and groove shapes. Head types include round heads, countersunk heads, and semi-sink heads.
6. Types of Self-tapping Screws
   
   • Ordinary self-tapping screws have a large pitch and are suitable for use on thin steel, copper, or aluminum plates or plastic.
   • Self-tapping locking screws are suitable for use in applications requiring vibration resistance.
7. Types of Washers:
   
   • Flat washers: Flat washers are used to overcome the unevenness of the support surface of a workpiece and increase the stress area of the support surface.
   • Spring washers: Spring washers rely on elasticity and friction to prevent the loosening of fasteners and are widely used where connections will not usually be disassembled. The inner tooth elastic washer and the outer tooth elastic washer have many sharp elastic warping teeth which are pressed against the supporting surface to prevent the loosening of the fastener.
   • Backstop washers: A backstop washer is a type of lock washer with either internal teeth or external teeth for locking.
   • Oblique washer: Oblique washers adapt to the inclination of a working bearing surface. Square inclined washers are used for inclined surfaces such as channel steel and I-beam flanges to avoid the bending force of the screw rod when the nut is tightened.
8. Type of Retaining Rings
   
   • 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 rings are installed in a groove on a shaft to hold a part in position. The steel wire retaining ring can only bear a small amount of axial force on the shaft.
   • Locking retaining rings for shaft parts: Locking retaining rings can be locked with taper pins and mainly used to prevent the axial movement of parts on a shaft.
   • Shaft end retaining ring: A shaft end retaining ring is fastened with screws and are mainly used to lock parts fixed to the end of a shaft.
9. Types of Pins
   
   • Cylindrical pins: Cylindrical pins are used to fix parts onto shaft to transmit power or act as positioning elements. Cylindrical pins are generally fixed into holes in the shaft and are usually not disassembled.
   • Tapered pin: Tapered pins are generally used as a positioning element where disassembly is not expected. They can be used in holes that do not pass completely through a material or in holes where it is difficult to drive a pin.
   • Cotter pin: A cotter pin is an anti-loosening device inserted into a hole in a nut or bolt. The pin is split into two feet which are separated after passing through the hole.
10. Types of Rivets
    
    • Hot forging rivets: Hot forging rivets are generally large rivets with heads formed by hot forging and are often used in locomotives, ships, and boilers, etc.
    • Cold heading rivets: Cold heading rivets are produced using die forms and punches that form metal wire into different shapes. This process is generally used for smaller diameter rivets of approximately 16mm.
    • Hollow and semi-hollow rivets: Hollow and semi-hollow rivets are used where little shear force is encountered. They are often used to connect non-metallic parts such as plastics, leather, wood, and canvas.