A cap screw is a threaded fastener that can be tightened or loosened by applying torque to its head. These screws have a shaft with an external thread that matches the internal thread of a tapped hole, allowing them to advance when rotated. Cap screws can be used without a nut and are often installed in metal-based applications, such as in automotive or aerospace projects. They are typically made from cold-formed or extruded metal and undergo various processes to improve their tensile strength, hardness and other properties. They are then finished, coated or plated to increase corrosion resistance and aesthetics.
There are several different types of cap screw, each designed for a specific set of uses. Hex cap screws (also known as hex bolts) have a six-sided hexagonal head that allows for greater torque than screws with a circular head. These fasteners can’t be installed or removed with a screwdriver bit, so they require a socket wrench and ratchet to install or remove them. These bolts are ideal for heavy-duty applications and are available in a range of sizes and grades, including hex head cap screws that can handle up to 180,000 pounds per square inch (psi).
Flat head socket cap screws have a recessed hexagonal drive hole, which means they can only be driven with a socket wrench or hex Allen key. These cap screws have a wide flange that acts like a washer, dispersing load around the bearing surface and helping to prevent them from crushing thinner or soft materials. They can also be countersunk, allowing them to lie flush with the material’s surface for a smooth finish.
Button socket cap screws have a lower profile, dome-shaped head and a recessed hexagonal drive hole that’s compatible with an Allen wrench. These cap screws have a flange that acts as a washer and disperses the load, but they aren’t as durable as other cap screw types.
These fasteners are often marked with identifying markings, such as ISO standardized sizes and hex head markings that indicate the fastener’s grade or tensile strength. The hex head markings may refer to the number of sides in the head, the diameter of the head, the length of the shank or the pitch of the thread. Grades include 2 and 5, with higher-tensile strength types like L9 used for high stress environments.
Socket cap screws are manufactured from a variety of materials, including metal alloys and stainless steel. They’re produced using either a cold-forming or cold-rolling process, which transforms the metal into its basic shape and creates the threads by pressing or cutting. Depending on the application, these screws may be heat-treated or hot-rolled to improve their hardness, tensile strength and other performance traits. They are then finished, coated or capped to increase corrosion resistance and enhance aesthetics. They can be used in a wide range of applications, from construction to electronics and automotive industry. These screws are often accompanied by washers and nuts to add support and help prevent loosening.