A flush bolt is a type of door hardware used to secure one of the two leaves in a pair of double doors (typically the inactive leaf) by sliding a metal bolt into the door frame or the floor. It is called a flush bolt because it is recessed or "flush" with the edge of the door, making it unobtrusive and keeping the door surface smooth.

Where It’s Used:

• Double Doors: Commonly used on double doors, where one door is active (operated with a knob or handle) and the other remains fixed. The flush bolt is mounted on the inactive door.
• French Doors: Often seen on French doors to secure one side while the other is in use.
• Commercial Buildings: Frequently installed on commercial and industrial double-door entrances for added security.
• Residential Applications: Used in homes on closet, pantry, or patio doors for a cleaner, sleeker look.

Flush bolts provide added security and help ensure that the inactive door remains stationary when necessary, without the need for visible latches or locks.