Most often used as additional security and vary in type and size according to application. There is the simple Sliding Barrel Bolt which is a manually operated low security deadbolt for the inside of a door, all the way through to the Mortice High Security Bolt or Rack Bolt (bolts fitted approximately 150mm (6") from the top and bottom of the door into the wood and operated internally) or surface-mounted locking bolts top and bottom. They should always be fitted at 90º to the grain of the wood, reducing the likelihood of the wood splitting if subjected to pressure.
