Gardall SL4000F Heavy Duty Concealed Wall Safe 1 each non-removable shelf is located right in the center (i.e 6 inches). The model SL4000F comes standard with a flange for easier and cleaner looking installation. The model SL4000F comes standard with a flange for easier and cleaner looking installation. This all steel construction wall safe has 1/8" steel body and a 1/4" solid steel door. It mounts easily into standard 16" wall studs (hardware is not included). A wall hanging easily conceals the safe. It also comes standard with a combination lock.