Defender Security U 10327 Door Knocker & Viewer, 9/16 in. Bore, 180-Degree View Angle, Satin Nickel Used on entry doors to provide privacy while viewing from inside the home, and also as a decorative door knocker for visitors Requires a 9/16 in. diameter installation hole, designed to install on 1-3/8 in. to 1-3/4 in. thick doors. Total height is 5-1/2 in. Satin nickel finish Diecast construction