An F-clamp, also known as a bar clamp or speed clamp and a "G-clamp", is a type of clamp. The name comes from its "F" shape. The F-clamp is similar to a C- clamp in use, but has a wider opening capacity (throat). This tool is used in woodworking while more permanent attachment is being. A bar clamp's main parts consist of two jaws, a bar, a handle and a screw. by either mm or mm, depending on the size of lengthening bar used. Define bar clamp: a frame consisting of a long bar with two adjustable clamping jaws that is used usually in woodwork or cabinetmaking for holding.