Choosing the Right Flush Bolt
A flush bolt provides a discreet way to secure one leaf of a pair of double doors.
Rather than sitting prominently on the face of the door, the bolt mechanism is recessed into the door so that the faceplate sits neatly with the surrounding surface.
Flush bolts are commonly used on double doors, French doors and commercial timber door sets, where one door leaf remains inactive until the full width of the opening is required.
When choosing a flush bolt, consider the bolt length, fixing position, door construction, required throw, finish and whether the door is fire rated.
Flush Bolts for Double Doors
On a pair of double doors, one leaf is normally designated as the active leaf and the other as the inactive leaf.
The inactive door leaf can be secured using flush bolts positioned towards the top and bottom of the door. The bolts engage into suitable keeps within the frame, floor or threshold.
Once the inactive leaf is secured, the active door can close and latch against it in the normal way.
This arrangement is commonly used on double entrance doors, internal double doors and commercial door sets.
Lever Action Flush Bolts
A lever-action flush bolt uses a small recessed lever to extend or retract the bolt.
When the lever is operated, the bolt projects into its keep to secure the door. Returning the lever retracts the bolt and allows the inactive leaf to open.
The recessed mechanism provides a neat appearance while remaining straightforward to operate when access to the full doorway is required.
Choosing the Correct Flush Bolt Length
Flush bolts are available in a variety of lengths.
Shorter bolts can be suitable where the operating lever remains easily accessible, while longer flush bolts are often used on tall doors or where the operating position needs to be brought within easier reach.
Before ordering, check the overall bolt length, faceplate dimensions, bolt diameter and bolt throw against the door and frame arrangement.
The location of other door hardware should also be considered before machining the door.
Square or Radiused Forend?
Some flush bolts are available with either a square or radiused faceplate, sometimes referred to as the forend.
A square-ended faceplate requires a square-ended recess, while a radiused version can suit door preparation carried out using an appropriate router.
Where replacement flush bolts are being installed, choosing a faceplate shape and size that closely matches the existing preparation can simplify installation.
Flush Bolts for Fire Doors
Selected flush bolts can be used as part of a fire-rated timber door assembly.
However, fire performance depends on the complete doorset and not simply on the bolt itself.
Where a flush bolt is fitted to a fire door, check the fire test evidence, required intumescent protection, permitted bolt position and manufacturer's installation instructions.
Machining a fire door to accept a flush bolt removes material from the door construction, so any specified intumescent protection around the bolt should be installed correctly.
Flush Bolts & Intumescent Protection
Certain fire-rated flush bolts require an intumescent pack around the bolt body.
Under fire conditions, the intumescent material expands and helps protect the area where the door has been recessed to accommodate the hardware.
The correct intumescent kit should be matched to the particular flush bolt and fire-door specification.
Do not assume that a generic intumescent strip can replace the hardware-specific protection required by the tested assembly.
Flush Bolts & Door Thresholds
Where a bottom flush bolt engages into the floor, a suitable keep or striking point is required.
Some door thresholds can incorporate dedicated flush-bolt striker blocks, providing a neat and defined point for the bolt to engage.
This can be particularly useful on double external doors where the threshold, seals and flush bolts need to work together as part of the complete door arrangement.
Choosing the Right Finish
Although most of a flush bolt is concealed within the door, the faceplate and operating lever remain visible when the door is open.
Choosing a finish that complements the surrounding door handles, hinges, locks and other ironmongery can therefore create a more coordinated door specification.
Options such as Satin Stainless Steel provide a clean commercial appearance, while Antique Brass, Satin Brass, Black and Dark Bronze can suit more decorative or traditional door schemes.
Frequently Asked Questions
What is a flush bolt?
A flush bolt is a recessed door bolt used to secure a door leaf.
It is commonly fitted to the inactive leaf of a pair of double doors and can engage into the head of the frame, floor or threshold.
What are flush bolts used for?
Flush bolts are primarily used to secure inactive leaves on double doors and French doors.
When the full doorway is required, the bolts can be retracted to allow both door leaves to open.
Do double doors need two flush bolts?
The inactive leaf is commonly secured at both the top and bottom, although the correct arrangement depends on the particular door set and specification.
For fire doors and commercial door sets, always follow the approved doorset configuration.
What is a lever-action flush bolt?
A lever-action flush bolt has a recessed lever that extends and retracts the bolt.
It provides a simple way to release or secure the inactive door leaf while maintaining a low-profile appearance.
Can flush bolts be used on fire doors?
Selected flush bolts can be used within fire-rated door assemblies.
The bolt must be suitable for the intended application and installed with any required intumescent protection in accordance with the relevant fire-door evidence.
What length flush bolt do I need?
The correct length depends on the door height, bolt position and how easily the operating lever needs to be reached.
Longer flush bolts can position the operating lever further away from the top or bottom edge of the door.
What is the bolt throw?
The bolt throw is the distance the bolt projects from its housing when fully engaged.
The keep, threshold or frame must provide sufficient depth and alignment for the bolt to engage correctly.
Can flush bolts be fitted into a door threshold?
Yes. Depending on the door arrangement, a bottom flush bolt can engage into a compatible threshold or dedicated striker block.
Always ensure that the threshold and bolt arrangement are designed to work together.
Need Help Choosing Flush Bolts?
The correct flush bolt will depend on your door construction, bolt position, required length, fire-door requirements and preferred finish.
Roundtower Hardware supplies flush bolts in Ireland for double doors, French doors, commercial doors and selected fire-rated timber door applications.
Browse our range online or contact our team if you need help choosing the correct flush bolt and associated intumescent protection for your door.
