Contract Door Security Bolt, sometimes called a Rack Bolt. The bolt is morticed inside the door edge and can be locked or unlocked via a separate splined key or with a fixed splined turn. The bolt has an internal sawtooth rack mechanism into which the splined key is inserted. The spline engages with the rack teeth and forms a gearing action which smoothly operates the bolt. KEYS SOLD SEPARATELY. Available Finishes: Polished Chrome, Satin Chrome Or Electro Brass. Dimensions: 85mm, 57mm Centres, Supplied Complete With Both Radius & Square Keep Plates. The Hex/Rack Style Keys Required To Operate These Door Bolts Are Sold Separately, Please See Related Products Below.