Steel or plastic housing. Steel box type is approximately 1 ¼" x ¾" x 2/3" Comes with integral brackets (to be directly affixed with screws or bolts) or without (needs a mounting bracket) Breakers have 10-32 studs, blades or wire leads Wire lead type has a 10" wire loop connected to studs and PVC-coated. Loop is intended to be cut, stripped and spliced into a circuit.