The wire bit is a .047\" spring wire (36\" long) that can be cut (at an angle) or length to make it the smallest reference bit. Its primary application is to be used as a reference point to measure from when having to drill in a specific wall cavity (i.e. drilling down through top plate in wall with stapled bat insulation, up from basement in wall with blown-in-cellulose or styrofoam insulation). The hole created is so small that it will remain unnoticeable, even on a ceiling. Includes pack of 10, 36\" long, .047\" diameter spring wire.