Secure your home or office doors with additional security with the U 10304 Chain Door Guard. This door chain lock is a security locking device for doors, allowing a door to be slightly opened to allow safe viewing and ventilation. It can also be placed out of reach of children, high on a door, so they cannot open the door themselves and enter or exit into dangerous areas. This chain door guard is constructed of extruded brass with a satin nickel plated finish and a 6 inch, 8-link welded steel chain It’s strong and durable, sure to last, and installation is quick and easy. All installation fasteners are included, and it can be used on a variety of door types and can be placed over or beside door casing. When this chain door guard is fully assembled, and engaged from base to keeper, the chain will extend to 4-5/8 inch. To determine the maximum distance the chain door guard secures a door for safe viewing or ventilation, subtract the thickness of the door from 4-5/8 inch(approx. 3 inch). The smaller chain-holder base measures ¾ inch wide, and the wider chain lock keeper measures 3-5/16 inch long; both with a height of 2 inch.