Yale's maximum security BS2 nightlatches are British Standard approved to ensure the highest level of security for timber external doors. They are Kitemarked to BS 3621:2007 and are recommended by insurance companies.  The lock is key operated from the outside and both key and lever handle operation from the inside with the internal handle being lockable for increased security. The latch automatically deadlocks on closing the door and the snib function enables the latch to be held back. The lock uses a 6 pin high performance cylinder, and has a 20mm bolt which is anti-carding. It also has a 10 year guarantee. The BS2 nightlatches have a 40mm backset, this is the measurement from the edge of the door to the centre of the keyhole. Locks with a 40mm backset are normally used where there is restricted space, such as on a glass panelled door Case Width: 89mmCase Height: 90mmCase Depth: 33mm.