Steel or plastic housing. Steel box type is approximately 1-1/4 x 3/4 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.