What’s a cap screw?

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Cap screws are fasteners used to secure machine parts and other objects. They have a large head and a cylindrical shaft with an external thread that matches the internal thread of a tapped hole. Cap screws come in different sizes, types, and materials, and generate high clamping force when tightened. They can be made of carbon steel, stainless steel, brass, metal alloys, or plastic. Choosing the right cap screw depends on the application’s environment and stresses.

A cap screw is a type of fastener used to make mechanical connections between mating objects, to ensure they are held together securely. These screws are commonly used to secure machine parts and many other types of objects, such as those inside household appliances or consumer electronic devices. It is important to select the right size and type of cap screw for each individual application.

A cap screw is screwed directly into a threaded or tapped hole and is normally used without a nut. It has a large head on one end and a cylindrical shaft with an external thread, a helical structure that allows the screw to advance when it is rotated. The tapped hole has an internal thread that matches the external thread of the screw. When this screw is inserted and turned into a threaded hole, it advances. The screw is tightened and loosened by applying torque to the screw head using a tool.

A variety of cap screw heads are available to allow you to use different tools to tighten or loosen the screw. The head has a larger diameter than the threaded portion to provide a positive mechanical stop when tightening the screw and to allow for shaping of the head to accept a specific type of tool. Examples of commonly used cap screw heads are the hex head, which has a hex shape for use with a wrench; the Allen head, which has a recessed hex hole for use with an Allen key; and the button head, which has a lower profile, domed head, and recessed hex bore for use in counterbore holes.

A cap screw can generate a high clamping force when tightened. The mating surfaces between the screw and nut resist the force applied by the screw and help prevent the mechanical connection from loosening over time. The type and size of cap screw chosen for a particular application depends primarily on the forces required to adequately secure the mechanical connection.

Cap screws are available in English and metric sizes and in a wide variety of coarse and fine threads. They can be made using carbon steel, stainless steel, or brass to resist corrosion; metal alloys for high strength applications; and also plastic materials. When selecting a cap screw, it is important to understand the environment and stresses to which the mechanical connections will be exposed so that the correct size and material are used.

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