Surface bolt has 1-1/4" throw for maximum security. Jimmy-resistant design, bolt locks automatically when thrown, can be released only by pressing knob toward door while retracting. Ideal for all types of doors. Unit locks in both the up and down position. Accepts padlock (not furnished) with maximum 3/8" diameter shackle, minimum 1-3/4" shackle opening height. Units packed with one-way wood screws for added security, standard wood screws also supplied. Units packed with a universal top strike (US). UL listed for 3 hour fire doors, up to 10'0'.