The single cylinder deadbolt locks and unlocks from the inside with a turn-button, and from the outside with a key. This is a Two Point Lock and requires 3 bore holes (see the installation instructions- PDF file) The Top Deadbolt is a Single Cylinder Deadbolt that operates the Deadbolt Latch by key from the exterior and by thumbturn (on the deadbolt)from the interior. The lower Deadbolt (just above the exterior thumblatch) operates the bottom spring latch from the exterior using a key and from the interior by the thumbturn on the Interior Wave Lever. Made of solid forged brass for maximum strength and durability. Latch is constructed for exceptional durability and smooth operation. They are reversible to accommodate all door conditions. All latches are supplied standard with a full lip strike. Deadbolt and latch bolt are constructed of solid brass for strength and security Concealed mounting system means that there are no fasteners visible to accumulate dirt and debris.