Flush Bolts are mounted in a door to lock a door in place. These Flush bolts slide up into the jamb above the door, and down into the threshold or floor below door. These are used primarily on double doors, where one door is locked in place and the other door is the one mainly used. When needed, the door locked in place can be opened. Flush bolts can also be called slide bolts, which are mounted to the face of the door. Flush bolts are mounted flush with the edge of the door.