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How to fit a bathroom door lock

Updated: October 2026

You have a drill, a bathroom or bedroom door, and either a surface bolt or an old sashlock cut-out. Those are two jobs. A slide bolt is a few screws into sound timber. A mortice sashlock has to match the hole, the latch bevel and the forend. This page is the sequence and the point where you stop. Prices stay on the [room door lock comparison](/hub/door-and-window-security/room-door-lock). Peter F. used those amazon.co.uk listings, ERA’s mortice sequence and a Yale fitting sheet in October 2026. If your lock has its own template, that template wins. A qualifying purchase can earn a commission at no extra cost to you.

You have a drill, a bathroom or bedroom door, and either a surface bolt or an old sashlock cut-out. Those are two jobs. A slide bolt is a few screws into sound timber.

Our top picks

QWORK QWORK rotate bolt

Best overall

QWORK QWORK rotate bolt
9.2/10about £5.95
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JelKen Jelken 75 mm slide bolt

Best value

JelKen Jelken 75 mm slide bolt
9.0/10about £3.79
View offer
XFORT XFORT 3-lever sashlock

Rank 3

XFORT XFORT 3-lever sashlock
8.2/10about £10.99
View offer
On this page
  1. 1.Fit a surface bolt
  2. 2.When the bolt binds or the screws fail
  3. 3.Swap a mortice sashlock like for like
  4. 4.Stop and get a joiner

Fit a surface bolt

Screw the bolt into solid timber, not the joint where the stile meets the rail. Door Superstore puts bathroom privacy hardware at about a metre from the floor. Mark the bolt and the keep with the door closed. Drill a small pilot for each screw. The Jelken listing, the best value at about £3.79, says a screwdriver or a drill and about five minutes, with six screws and 4 mm holes on a 75 × 35 mm body. Reviews still report the bolt sticking once the screws are pulled tight. YUOIP specifies six M4 × 16 mm screws. If the pack looks short, use your own screws of a similar gauge. The QWORK rotate bolt, the top pick at about £5.95, is the same idea with a turn. One review says the jamb was routed so the keep sat flush. If the keep stands proud, you need a shallow recess, not a longer screw. Measure before you buy a case, using the internal door lock buying guide.

When the bolt binds or the screws fail

A bolt that sticks after you tighten it is usually the keep. Slacken the screws, close the door, and slide the bolt until it enters without force, then mark that position. Jelken reviews include a bolt that stuck and locked the writer in the bathroom. YUOIP reviews include a slide that catches when the parts are out of line. lmytdo reviews include screw heads that snap and a broken shank left in the timber. Do not keep driving the stump. If the bolt has already trapped you, take it off. An inside-only bolt has no landing-side release. What a proper emergency release looks like is on the bathroom door lock page.
QWORK QWORK rotate bolt

Testsieger

QWORK QWORK rotate bolt
9.2/10about £5.95
View offer

Swap a mortice sashlock like for like

Take the old case out before you cut anything new. Match the case depth, the backset, the forend length and whether the forend is square or rounded. ERA’s sequence is to mark clear of the rail joint, drill overlapping holes to the case depth, pare the mortice, recess the forend flush, and check that the latch bevel faces the frame. Yale’s 2-lever sheet gives a rule of thumb of about 68 mm drill depth for a 64 mm case. Drill the face holes from both sides. XFORT, at about £10.99, is the sashlock in this set. Reviews that matched an existing cut-out describe a straightforward swap. Others report a square forend when a round end was expected. The listing gives no drill diameter, so do not invent one. Handles are not in the box. Which listing is worth opening is on the best bathroom door lock page.

Stop and get a joiner

Stop if you do not know the door. GOV.UK says a fire door must close fully into the frame, and London Fire Brigade guidance notes that modifications can sit outside the doorset’s evidence. A new mortice or a bolt screwed through a certified door is not a casual afternoon. Stop if someone is locked in. A surface bolt cannot be undone from the landing. Stop if the new case does not match, or if the door has dropped onto the seals. A like-for-like bolt on a plain internal door, into sound timber, is the part you can finish yourself.

Common questions

How high should a bathroom bolt sit?
About a metre from the floor is the height Door Superstore uses, where an adult can reach the bolt and see it. Keep it on solid timber, clear of the rail joint. If a child can reach that height, an inside-only bolt is the wrong product.
What tools do I need for a slide bolt versus a sashlock?
A slide bolt needs a pencil, a tape, a small pilot drill and a screwdriver. A sashlock swap needs those plus a bit long enough for the case depth, a chisel, and the old lock as the template. Yale’s depths are a rule of thumb for Yale cases.
The bolt sticks after I tightened it. What now?
Slacken the screws, close the door, and let the bolt find the keep before you tighten again. Jelken and YUOIP reviews both describe binding when the keep is out of line. If it has already trapped someone, remove it from the bathroom door.
How do I know the latch bevel is the right way?
The sloping face must point towards the frame, so the door pushes the latch in as it closes. ERA’s sequence puts that check in before you fix the forend. If the square face hits the strike, turn the case over.
The new forend is square and the old recess is round. Can I force it?
No. XFORT reviews include a square forend where a round end was expected. Forcing it leaves the case proud. Recut the recess only on a door you may alter, or return the lock. Handles are not in the XFORT box.
When do I stop and call a joiner?
Call one if the door might be a fire door, if someone is locked in, if the new case does not match the mortice, or if the door has dropped and no longer meets the seals. A few screws for a bolt on a plain internal door is the job that stays with you.

Related pages

Bathroom door lock

Internal door lock buying guide

Room door lock

Best bathroom door lock: QWORK pick, Jelken value

Child proof door handle lock for a lever 2026

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk figures in this comparison. None of the ten listings is treated as BS 3621, BS 8621 or Secured by Design.

  1. GOV.UK: Fire Safety (England) Regulations 2022 fire door guidance (retrieved October 2026)
  2. BSI: BS 3621 scope (retrieved October 2026)
  3. BSI: BS 8621 scope (retrieved October 2026)
  4. Secured by Design: locks (retrieved October 2026)
  5. Lloyd Worrall: BS EN 12209:2016 digit guide (retrieved October 2026)
  6. London Fire Brigade: GN 92 (retrieved October 2026)
  7. ERA: how to fit a mortice lock (retrieved October 2026)
  8. T.H. Wiggans: bathroom door locks (retrieved October 2026)
  9. BABYGO: door handle lock (retrieved October 2026)