What Is a Cap Screw?

Cap screw, also known as hex screws or hex bolts, are used in many commercial and industrial projects. They are available in various grades, materials and sizes to meet the demands of specific applications.

They can withstand large forces and have an impressive clamping strength. They are a good choice for precise applications like an OEM setting and other projects that require tight tolerances.
Materials

The materials used to make cap screws vary according to the environment and stress they will be exposed to. They can be made from carbon steel, stainless steel, or metal alloys that offer corrosion resistance. They can also be made from plastics that provide lightweight, high-performance solutions.

Grade 8 cap screws are usually made from medium quality, heat-treated carbon steel. They are ideal for applications that require a controlled clamp force and high loads. They are often used in assembly lines and industrial production. They can be identified by the standard markings on their hex heads, which indicate the bolt’s grade.

Hex cap screw heads are available in a variety of shapes, sizes and finishes. They can be shaped to accept a specific type of tool or designed to fit in a socket wrench head. Various standards exist worldwide that ensure the quality, safety, and interoperability of these fasteners. These include hex head, recessed hexagonal, and button head.
Threads

In the United States, cap screws are commonly used in precision applications. They have hex heads and a flat washer facing under the head that meets specific tolerances as defined by ASME B18.2.1. They can be manufactured from a variety of materials, including carbon steel and stainless steel for corrosion resistance; metal alloys for high-strength applications; and plastic materials.

The threads on hex cap screws are cut and rolled and comply with the Unified Thread System (UTS). These are right-handed threads, meaning they turn clockwise when tightened. They are also available in a variety of sizes and lengths.

The thread helix angle is the angle that the thread forms around the helix of the screw. It is often measured using a thread gauge or a screw gauge. The helix angle is important for determining the accuracy of a thread’s fit. It can be determined by measuring the distance between the major diameter and the minor diameter of the thread.
Heads

Unlike standard hex screws, socket head cap screws have a large cylindrical head with a recessed hexagonal socket that accepts a spanner wrench or Allen wrench. This design allows them to be used in applications where clearance is limited and wrenches or sockets can’t be maneuvered into position.

The head also has a projection that acts like a washer to disperse the load across the bearing surface, and it has a chamfered point that helps prevent loosening from vibration. They also come with a nylon patch bonded onto the threads that increases locking strength.

Socket head cap screws are available in a variety of materials and sizes to meet a broad range of industry requirements. They’re often used in assembly, die fixturing, and clamping applications. They require proper installation and regular inspection to avoid damage, corrosion, or loosening. In addition, they need to be properly cleaned and lubricated to decrease friction during operation. They must be replaced promptly if they show signs of wear or damage.
Clamping force

The clamping force of a Cap screw is the amount of pressure it exerts when tightened. This pressure helps prevent the mechanical connection from loosening through vibration and other environmental conditions. The type of Cap screw selected for a particular application depends on the required clamping force.

Button socket cap screws have a curved design and provide a greater under head area to protect mating parts from scrapes and damage. These screws are ideal for applications where space is limited and wrenches or sockets cannot be used.

Hex socket cap screws have a recessed hex-shaped drive recess that distributes turning force evenly across six sides of the head. This makes them less likely to strip than traditional screws. Hex cap screws also offer a larger driving surface for increased torque and strength.