These ID clamps allow for holding the inside of workpieces. The steel jaws are forced outward as the cap screw is tightened. Because the clamp expands and wedges against the I.D. of the workpiece, they are ideal for parts were there may be variations in the inside diameter of the part such as cast iron or rough finish holes. The clamp makes a line at contact with the workpiece in the clamping mode. The contact can mar the surface of the workpiece depending on the material. Using these clamps for accurately finished holes is not recommended. The body is made from alloy steel, hardened with a black oxide finish. The springs are made from stainless steel.