A cap screw (cap bolt) is a type of screw with a cylindrical (cap-shaped) head that has a hexagonal socket. It is officially called a “hex socket head bolt” or “hex socket head cap bolt.” Typically, it is tightened and loosened using a hex wrench and is widely used in industrial applications and machinery assembly.

Overview of Cap Screws

Main Features

Cap screws (hex socket head bolts) and set screws (grub screws) are characterized by their hexagonal socket drive shape, allowing for high torque tightening. The hexagonal socket allows for even distribution of tool pressure at six points, reducing wear on the drive socket during fastening.

They are one of the most common types of screws, along with machine screws and hex bolts. Cap screws are primarily made of steel, with materials such as S45C and SCM435 undergoing heat treatment for increased hardness.

Main Applications

Cap screws are used not only for fastening machinery and equipment but also in applications where frequent fastening and loosening are required. While screws typically wear out over repeated use, cap screws withstand repeated fastening due to their hexagonal socket shape and heat-treated strength.

Types of Cap Screws:

• Cap (Hex Socket Head Bolt)
• Button Cap
• Countersunk Cap
• Set Screws (Cup Point, Flat Point, Cone Point, Dog Point, Double Point)
• Ball Plunger
• Plug
• Shoulder Bolt
• Air Vent Cap

Choosing the right type is essential depending on the environment and application.

Role of Cap Screws

Usage Scenarios

Due to their ability to handle high torque and frequent fastening, cap screws are commonly used in manufacturing jigs, vises, and mold fastening.

They are also widely used in machinery and equipment where high-torque fastening is needed. The hexagonal socket shape allows end users to fasten with minimal tools.

Examples of Applications:

• Cap (Hex Socket Head Bolt): Mold and jig fastening, high-torque applications, designs requiring minimal tools for assembly.
• Button Cap: Mold and jig fastening, high-torque applications, assembly with minimal tools.
• Countersunk Cap: Mold and jig fastening, high-torque applications, assembly with minimal tools.
• Set Screws (Cup Point, Flat Point, Cone Point, Dog Point, Double Point): Component assembly.
• Ball Plunger: Used for positioning, indexing, and ejecting sliding or rotating parts.
• Plug: Used in hydraulic and pneumatic equipment, pumps, and automobiles to stabilize airflow and oil flow.
• Shoulder Bolt / Stripper Bolt: These bolts have a long shank with a precision ground finish. They are commonly used for shaft fixing in moving parts, as well as in engines, pulleys, and vacuum systems.
• Air Vent Cap: Used mainly in semiconductor devices requiring a vacuum environment, featuring a hole through the bolt head for gas venting.

Conclusion

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