Impact-Resistant Thermoplastic Nylon Cover and Body * Smooth Face Does not Collect Dirt * Single-Piece Brass Mounting Strap on Extra Heavy-Duty Devices, Multi-Piece Steel Strap on Heavy-Duty Devices * Large, Triple-Wipe, Brass "T" Contacts for Superior Contact and Conductivity * Exclusive V-Shaped, Serrated Back-Wiring Clamps for Superior Contact and Conductivity