The concealed terminal-style surface mount switch sets are suitable for residential and commercial installations, setting an industry standard for commercial and light industrial applications. They can be mounted on a steel surface with minimal gap penalty, offering a choice of gap sizes: up to 1" (5/8" on steel) standard, up to 1 1/2" (3/4" on steel) wide, or up to 2" (1" on steel) extra wide gap.