S. Parker Hardware 1601VK Polished Brass Plated Glass Lenses Keystone Door Viewer With Knocker. The 1601 VK Glass Lenses keystone door interviewer with knocker offers a 190 degree view, has frames for name or apartment number, and is polished brass plated. The door interviewer fits doors from 1 3/8" to 2 1/8" thick. Used To Allow A User To Identify Visitors From The Security Of A Locked Door. PACKED 10 PIECES.