Bolts are mechanisms that keep doors secure, and locked. Flush bolts are a particular type of bolt that is flush, or even, with the side of the door. A manual flush bolt requires someone to lock, and unlock it manually. An automatic flush bolt depends on the opening, and closing of a double door to operate properly. Manual flush bolts are common on French-style doors, while automatic flush bolts are common on doors used as fire exits. Doors that must remain unlocked, but closed, during business hours commonly utilize automatic flush bolts.
Flush bolt installation requires two flush bolts laying even with the edge of the door. One of the bolts should be on the top of the door, and the other should be positioned on the bottom of the door. The bottom and top edges of the door must have holes for the bolt to extend through to pass into the space within the door jamb. The deadbolt is located in between the top, and bottom flush bolts. Automatic flush bolts can be installed on wood doors or aluminum doors.
In a set of double doors with automatic flush bolts, one of the doors is active and one is inactive. The active door is the door with the handle or push lever that opens the door. This is also the door with the dead bolt or other locking device. The inactive door is the door with the automatic flush bolts. These types of doors are commonly seen in schools, and hospitals and act as one of the main exits out of the building. For this reason, many states have laws governing the use of automatic flush bolts on fire exits.
When the double doors are closed, the automatic flush bolts only allow the active door to open. Once the active door opens, the flush bolts release and the inactive door unlocks and is free to open. Upon the active door closing, the automatic flush bolts will snap back into place making the active door the only side that can be opened.