A C-clamp or G- clamp is a type of clamp device typically used to hold a wood or metal work-piece, and often used in, but are not limited to, carpentry and welding. These clamps are called "C" clamps because of their C shaped frame, but are otherwise often called G-clamps or G-cramps because including the screw part they are shaped like an uppercase letter G. The fixed end is not adjustable so size is not variable.
G-clamps are typically made of steel or cast iron, though smaller clamps may be made of pot metal. At the top of the "G" is usually a small flat edge. At the bottom is a threaded hole through which a large threaded screw protrudes. One end of this screw contains a flat edge of similar size to the one at the top of the frame, and the other end usually a small metal bar, perpendicular to the screw itself, which is used to gain leverage when tightening the clamp. When the clamp is completely closed, the flat end of the screw is in contact with the flat end on the frame When used some other object or objects will be contained between the top and bottom flat edges.
A steel 'G' Clamp