This flush bolt is fitted so that it is flush with the face of a door. The door surface has to be cut away to house the body of the bolt. Flush bolts can be fitted to the external face of a door but more usually are fitted into the leading edge of the door, so that when a pair of doors are closed, the flush bolt is fully concealed. This can increase security. A flush bolt is used to bolt the inactive leaf of a pair of locked double doors.