The M.Marcus Roller Bolt Nightlatch Satin Chrome is preferred for flat front doors and dwelling with only one entrance. When the door closes the roller bolt will engage but not deadlock. The deadlock function does not operate until either the key is turned externally or the internal lever is rotated.  Hence, it is impossible to lock yourself out of your own flat, something that happens in many instances when the door closer, closes the door automatically. This roller bolt nightlatch has a cylinder backset of 60mm. Other Variations This nightlatch is also available in the foll...