Auth Florence, Non Electric, Mechanical Door Chime, Doorbell and Viewer #689 (Silver Powder Coated Metal) High quality, maintenance free, no wiring, no batteries, one way viewing mirror. Designed to fit wood and steel doors up to 4-3/4" thick. Requires to drill 5 holes through the door. Mounting and fastening hardware includes only screws for wood doors. We manufacture and include self drilling screws for steel doors. (see the self drilling screws in the pictures above).