Machine screws are small screws designed to be fastened into an existing threaded hole in a metal surface with a matching nut. They come in different sizes, head shapes, groove types, lengths, materials, and thread characteristics. The type of slot in the head determines the type of screwdriver needed. The thread characteristics follow ISO standards, including diameter, pitch, and direction. Machine screws can be made from various metals or plastics and can be customized for specific machines.
A machine screw, also sometimes referred to as a machine bolt, is a screw that is typically designed to be fastened into an existing threaded hole in a metal surface, usually in conjunction with a matching nut. These types of screws are not as large as the average screw, usually up to three-quarters of an inch (19.05 mm) in size, but can still be larger. Variations among machine screws exist primarily in overall dimensions, head shape, groove type, length, material, and thread characteristics.
An important way to classify a machine screw is the type of slot in the head, which will determine the type of screwdriver that needs to drive it into its hole. The two main types of screwdrivers used with machine screws are the slotted and Phillips screwdrivers, but there are many other minor types of screw holes such as Torx – star-shaped, six-pointed screw holes – that require more specialized screwdrivers . Special types of screw holes can be important when you don’t want the screws to be interfered with for safety reasons, as specialized types of screwdrivers are more difficult to acquire. A dangerous electrical panel, for example, is a good place for a machine screw with a special type of hole. Other machine screw heads can be similar to a hex or square bolt that doesn’t have a screwdriver slot and must be turned with a wrench.
The shape of a machine screw’s head will determine how it sits when it is fastened into a hole. The round, pan heads protrude from a flat surface when attached. Thumbscrews are designed for drilled holes so that they sit flush with the surface when screwed in. The head of a set screw is smaller than the diameter of the screw threads, so when set it can be driven through a hole and set to the desired depth.
Most of the main differences between machine screws lie in the characteristics of the thread. This part of a given machine screw is one of the most important, because the corresponding holes into which they are attached will typically be tapped to fit only a specific size and type of screw thread. The system used to characterize the different threads usually follows the International Organization for Standardization (ISO) standards, which were established to keep design specifications consistent in machine parts manufactured around the world. Two of the main characteristics of the thread are the diameter and the pitch, the latter being the distance between the threads. These threads can also be made to be screwed in clockwise (right hand) or counter clockwise (left hand).
Although the dimensions of a machine screw are generally relatively small, there can still be a large amount of variation between size, shape and length, mainly determined by their intended purpose and their robustness. Custom screws can also be manufactured for specific machines that don’t even have to follow any ISO standards. Machine screws can be made from a variety of metals or plastics.
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