SM-4Z, SM-5S, SM-5SS, and SML-4Z Power Fuses consist of a mounting and a removable holder(s) containing a replaceable refill unit. SM-20, SM-40, and SML-20 Power Fuses consist of a mounting and a replaceable fuse unit assembly.

The mounting includes the following:

Rugged 3/16-inch thick flanged, formed steel base
Cypoxy™ station post insulators
Two-hole terminal pad
Bifurcated, spring-backed upper and lower contact assemblies are copper, heavily silver-clad
Zinc-plated hot-rolled steel or cast-bronze hinge on disconnect style mountings. On non-disconnect style mountings, bronze hangers and stick-operated clamps support and retain holder

SML-20 and SML-4Z Power Fuses also include:

Uni-Rupter™ which provides 200-ampere single-pole live switching
Fault-closing contacts that provide duty-cycle fault-closing ratings