Nylon Rivet 1/4″ Diameter 5/32″-3/8″ Grip Black • Rivets: Used for attachment in many different areas. The critical dimensions are the diameter of the rivet body and the grip range or panel thickness. There’s no way to determine what the grip range is by measuring the rivet. That’s an engineered specification that has to be given. Rivets can be made of steel, stainless steel, aluminum or nylon (usually black). The mandrel is the part that breaks off when the rivet is installed.