This CRL Clamp-On Frame Interior Window uses the Surround Sound Voice Transmission System for unobstructed viewing through the glazing material. Designed for installation in wall thicknesses from 5" to 8-1/2" (127 to 216 mm). Screws fastened through the interior side of the frame clamp the window securely in the opening. Supplied with a 12" (305 mm) deep Stainless Steel Shelf with Non-Ricochet Bullet Resistant Deal Tray. Glazing is 1-1/4" (32 mm) thick bullet resistant acrylic rated for Level 1 protection. Two finishes are supplied in two stock sizes.