Taparia Hand Tools Accessories, 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 made with screws or glue, or in metalworking to hold pieces together for welding or bolting.