This Siemens U-EC-S17-W Chime Strobe comes designed for use with either a surface or flush grille and can be use with different accessories for a variety of mounting applications. Besides, the U-EC-S17-W basic chime strobe is furnish with two #8-32 x 1″ screws for mounting the horn to a 4-inch square backbox or to a weatherproof box. The terminals are design to accept up to 12# Ga. wire. Also, the Siemens U-EC-S17-W is list for indoor use; mounts a ceiling grille to the basic horn mechanism with the 1/2-inch mounting screws. This assembled unit must mount directly to a standard 4-inch square flush back box.