The Essentials of Flush Bolts
Flush bolts are installed into the lock stile on the inactive leaf of a pair of doors. There are often two bolts, one installed at the top and one at the bottom of the door. The strike of the top bolt will be in the head of the frame and the strike for the bottom bolt will be in the floor. Other door hardware used on the opening must be compatible with the type of flush bolts you use. Building codes and life safety requirements may also restrict the type of flush bolts you can use.
Manual Extension Flush Bolts
Manual flush bolts require a person to manually retract the bolts by flipping a small lever that pulls the bolt in. The bolt is held retracted until a person manually re-latches the door by moving the small lever to extend the bolt into the strike.
Manual extension flush bolts are available for both wood and hollow metal doors. Wood doors will have the top corner mortised to receive wood door flush bolts. When the wood door flush bolts are used it can sometimes weaken the top corner of the wood door. Also, because they are positioned at the top corner of the doors, they can be harder to reach, so manual wood door flush bolts are not used as often. Fortunately, wood doors can also be prepped to receive metal door flush bolts.
Metal door flush bolts have longer rods which lowers the height of the lever used to retract the bolts. The standard length for these rods are 12″ but they can be extended to 18″ up to 24″ and sometimes even 48″. The height of the door can determine the length of rod that will be used.
Self-Latching Flush Bolts
Self-latching flush bolts are often called constant latching flush bolts. These bolts are a combination of the manual extension flush bolts and automatic latching flush bolts. The top bolt must be manually retracted by a push-button or slide in order to open. However, unlike the manual flush bolts that holds the bolt retracted, the constant latching bolt is spring-loaded and projects itself back out when the slide or push-button is released.
Additionally, the constant latching top bolt has a beveled face, similar to a latch on a bored lockset. When it comes in contact with the lipped strike it will re-latch by itself. If a top bolt and a bottom bolt are used, the bottom bolt will be an automatic latching flush bolt.
Automatic Flush Bolts
Automatic flush bolts are projected and retracted without any manual operation required. When the active leaf is opened, the flush bolts are retracted, allowing the inactive door to open. When the active leaf is closed, the flush bolts are automatically latched again.
This automatic latching is accomplished by a small spring-loaded button on the edge of the flush bolts which, when depressed, will extend the flush bolts and remain latched. When the active leaf is opened, these buttons will protrude from the edge of the door which pulls the flush bolts to the retracted position. When the active door is shut again, it will push these buttons and cause the bolts to re-latch.
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