Glossary Terms - B

Back Check

A feature in many hydraulic door closers that may be adjusted to slow the opening movement of the door, taking effect usually between 60 to 85 degrees of opening. It is intended to protect objects from forceful door openings impacts. It should always be used in conjunction with a doorstop to protect the door and door hardware. Optional advanced back check may take effect as early as 45 degrees of opening.

Back Check Location

The point (approximately 70º) in the opening cycle where backcheck takes effect.


Backset (of a lock or panic device) – The distance from the centerline of a knob or lever hub, keyhole or cylinder to the face of  the lock (latchbolt face) on the edge of the door. When a beveled door is used the measurement is always taken from the high bevel side.


Big Blue Flash - Usually what happens when a product is supplied too much voltage. Kills product and sometimes hurts people.


Bevel (of a lock) – Term used to indicate the direction the latchbolt is inclined; egular bevel for inward opening doors and reverse bevel for doors opening outward.

Bevel (of a lock front) – Refers to the face of the latch when it is not at 90 degrees to the lock case. This is necessary for a flush fit with the corresponding beveled door edge.

Beveled Edge

The edge of a door that is not at a 90-degree angle to the door face. The usual bevel on most doors in indicated as 1/8 inch in 2 inches (3.2mm to 50.8mm). The narrow side of the door is considered the leading edge and is in contact with the stop of the frame when the door is closed.


Builders Hardware Manufactures Association

Bicentric Cylinder

A cylinder having two independent plugs, sometimes with different keyways. Both plugs are operable from the same face of the cylinder.


The use of unique biological characteristics, such as a fingerprint or iris, to manage access.


Bit (of a key) – The cut(s) made in a key blanks blade that actuates the pins (tumblers) within a cylinder, allowing the cylinder to operate.

Bitting Numbers

The numbers that represent the depths of the cuts made in a key blank, necessary to operate a cylinder as scheduled.

Blocking Bar

A spring loaded bar located within the cylinde shell extending parallel to the keyway that when activated by a key with the proper machining, allows for a shear line between the cylinder shell and plug. When the wrong blank is inserted into the cylinder the blocking bar inhibits the rotation of the cylinder plug even if the combination of the key biting is correct to operate the lock.

Blockout Cylinder

A cylinder which allows all keys to be temporarily blocked from operating. It is set by a blockout key.

Bored Lock

A lock or latch that is intended for installation in cylindrical holes bored into a door.

Borrowed Arm

A hardware arm mechanism that is mounted on the bottom rail of a door and is then connected to the spindle or pin of a floor closer or pivot.

Bottom Rail

The horizontal rail at the bottom of a door that connects the lock stile and hinge stile. On a Stile and Rail type door this component would be visible. On a Flush type door the stile would not be a totally visible feature.


Bow (of a key) – The enlarged part of a key that is used as a turning grip.

Box Strike

A strike that incorporates a covered housing to the sides and back of the strike to protect the bolt when projected into the strike.