Pack of 4 restrictors for venting sash windows. It also acts as a sash restrictor. Pack Includes Strike Plates, Insertion tool and Screws. The restrictor was developed for home security & ventilation. It allows the sash to be left open a few inches without compromising security or safety. This product is NOT lockable. You use the tool to insert it and when you remove the tool, the barrel spins rather than undoes. You use the tool to remove it again.