The storeroom function always requires a key to open the door from the outside, the inside remains unlocked. Constructed with a robust cylindrical locking mechanism, this lock is designed for heavy use doors. It is extremely robust mechanically and has a durable finish. This lock is also versatile and can fit doors from 1-3/8 in. to 2 in. T. It is UL listed for 3 hour doors. It meets or exceeds ANSI Grade 2 standards and is ADA compliant.