Auth Florence, Non Electric, Mechanical Door Chime, Doorbell and Viewer #686 (Anodized Silver Aluminum) High Quality, Maintenance Free, No Wiring, No Batteries, One Way Wide Angle Viewing Lens. Designed to Fit Wood and Steel Doors up to 4-3/4" Thick. Requires to drill 2 holes through the door. (see the template in the pictures above). 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).