With its truly unique design, the MUL-T-LOCK Hercular deadbolt is truly spectacular. The Hercular is reinforced in just about every way possible. From a UL437 Listed Cylinder to a strong latch to Bolt Bearing Mechanism the Hercular Deadbolt will stop almost any attempt at forced entry. Strength usually does not mix with Flexibility. Not in the case of the Hercular since it is the only Grade 1 Deadlock with an adjustable backset.