Latch bolt operated by lever from either side axcept when outside lever is locked from outside by key. When outside lever is locked, latch bolt retracted by key, or by operating key and outside lever fromoutside or byoperatinginside lever. Auxiliary dead latch. Mortise Entry Lock Set DDAL04 F04 delivers high-security performance for office entry doors requiring ANSI Grade 1 reliability. Engineered with a full stainless steel structure, this lock set ensures consistent durability under high-frequency commercial use. The integrated auxiliary dead latch enhances protection against forced entry, meeting strict safety expectations in commercial environments. With UL fire-rated certification, the lock maintains structural integrity under fire conditions, making it suitable for projects where compliance and safety are critical. Precision machining and standardized dimensions allow easy integration into American standard door systems, supporting both left-hand and right-hand installations. From daily office access control to high-traffic commercial buildings, this mortise entry lock set ensures reliable performance, consistent quality, and long-term stability required by professional door hardware applications.