Why buy a knob lock that can be locked with a key on both sides? Secure spaces make for joyful people and productive working environments. This stainless steel knob set is conveniently designed to work with keys on both sides for enhanced security! This is especially true for doors that have glass panels or adjacent windows (i.e. an arm’s reach). An intruder could unlock the door by breaking the glass and reaching inside. Installing double cylinder locks on exterior doors eliminates this problem. Since there is no thumb-turn, intruders cannot reach inside to unlock doors manually through broken windows, maybe get a nasty gash trying. A back to back cylindrical mortise deadlatch providing keyed access in both directions. The outside knob will either simultaneously lock or unlock both ends of the lock after a key is used. The spring-loaded latch bolt will not lock automatically when the door is closed unless the key is used again or left in a locked position. It's non-handed, fully reversible for right or left-handed doors. Made with highly durable steel & brass components. This makes an excellent connection to any standard door prep. Architectural design blends in with most door decorative hardware. Installation by Phillips screwdriver. Includes one adjustable ANSI grade II cylindrical 2 3/4" (70mm) and 2 3/8" (60mm) backsets. For door thickness 1 1/4" - 1 13/16". Six-pin re-keyable cylinder equipped with mushroom pick resistant and anti-bump driver pins profile. Perfectly suited for aluminum and wood doors. 100% guaranteed in materials and workmanship. ATTENTION: IF YOU ARE NOT HANDY WITH LOCK HARDWARE COMPONENTS, PLEASE CONSULT WITH A CERTIFIED LOCKSMITH! Buy this hard-to-find knob lock Today. Don't just lock it...SECURE IT!