JT&T"s Santoprene Insulated Clamps are made with cold rolled steel and have a 1/4" mounting hole. Santoprene is a superior material in areas of friction, grip effort, surface texture, perceived control, finger comfort and hand comfort in comparison with grips made of steel or polypropylene. Other attributes include soft-touch, durability, resistance to heat and various fluids. Santoprene is an excellent insulator for electrical installation and provides a consistant thickness throughout. JT&T Products offers a complete line of popular santoprene clamps and also nylon cable clamps.