S. Parker, Non Electric, Mechanical Door Chime, Doorbell and Viewer (Dull Chrome) High quality, maintenance free, no wiring, no batteries Designed to fit wood and steel doors from 1/4" to 2" thick 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). Requires to drill 2 holes through the door, 1-3/4" and 1/2" diameter