Bullet resistant window fits into rough wall opening and clamps onto finished wall. Extruded aluminum frame adjusts for walls 5" to 8.5" thick. Window unit clamps into place with bolts positioned through back frame into threaded section of front frame. Glazing is held in place with rubber spacers, providing space around sides and top for natural voice transmission. Stainless steel shelf with built-in tray is fastened into frame. Choice of glazing. Entire unit is shipped fully assembled. This model is for interior use only.