From The Anvil Black 2 1/2' BS 5 Lever Deadlock
Sizes: Case Depth: 64mm Backset: 44mm Case Height: 80mm Forend Length: 139mm Forend Width: 26mm 20mm solid steel anti-thrust, anti-saw, anti-drill bolt throw. Supplied with 3 keys as standard with box striking plate and fixings. Complies with British standard - BS3621:2004. Supplied without escutcheons - must be purchased separately.
Can be used as an additional lock below the rim lock. It will provide extra security and compliance for insurance purposes.