Bolts can be used to provide additional security on external doors fit both top and bottom of the door. Barrel, padbolts and tower bolts can be screwed on the surface of the door. Each has a bolt which is generally long shot to be the principal (the ring of metal) fixed to the door frame. Always choose a bolt with a principal-and long heavy duty screw fix. Alternatively, bolts can pass through the jamb or the floor or into the doorframe.