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How to fit mortice door knobs on a timber door

Updated: October 2026

You have a screwdriver, a pair of round knobs, and a timber door that already latches. How to fit mortice door knobs, in the like-for-like case, is a measurement job first and a screw job second. You should finish knowing the spindle size, the backset, and the moment to stop because the door is a fire door or the lock is the final exit. This is not a ranking, and it is not the choice of an emergency release. Prices are on the [doorknob comparison](/hub/door-and-window-security/doorknob). Which set type you bought is on the [doorknob buying guide](/hub/door-and-window-security/doorknob/sub/doorknob-buying-guide). Peter F. used the amazon.co.uk review record, updated October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You have a screwdriver, a pair of round knobs, and a timber door that already latches. How to fit mortice door knobs, in the like-for-like case, is a measurement job first and a screw job second.

Our top picks

Infinity Decor Infinity Victorian brass knobs, 52 mm

Best overall

Infinity Decor Infinity Victorian brass knobs, 52 mm
7.8/10about £16.95
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HANDLESTORE Handlestore polished chrome sprung pair

Rank 2

HANDLESTORE Handlestore polished chrome sprung pair
8.6/10about £10.99
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Sterling Sterling SRL8BK black rim pair

Best value

Sterling Sterling SRL8BK black rim pair
8.2/10about £6.99
View offer
On this page
  1. 1.Check the door before you open the box
  2. 2.Measure backset and spindle
  3. 3.Mortice pair, then the rim difference
  4. 4.When it is stiff or the screws scratch

Check the door before you open the box

The household case is a timber door that already has a working latch or a rim lock, and a new pair that matches it. A fire door, or the lock on a final exit, is a different job. If the door carries a fire or smoke label, put the screwdriver down and call a joiner or a Master Locksmiths Association locksmith. On an ordinary internal door, confirm a latch is actually in the edge. The polished chrome pair and both Infinity brass pairs supply knobs, a spindle and screws. They do not name a latch. If you only discover that after the old knobs are off, the door will not stay shut. Several listings quote 35–45 mm. Measure the stile.

Measure backset and spindle

Backset is the distance from the edge of the door to the centre of the spindle, not the inch length printed on the latch case. More Handles puts a 76 mm case at about 56 mm of backset. Makers differ by a few millimetres, so measure your own door. A short latch leaves your hand on the architrave. The spindle is the square bar through the follower. Modern UK latches are commonly 8 mm. Older rim locks sit nearer 7 mm. Infinity’s Victorian pair prints 125 × 8 mm, so you can hold that bar up to the old follower before any screw goes in. XFORT reviews describe a bar that was slightly too thick. If the bar will not enter, the set is the wrong follower size. The mortice or rim doorknob page is the fork if you are still unsure which case is on the door.
Infinity Decor Infinity Victorian brass knobs, 52 mm

Testsieger

Infinity Decor Infinity Victorian brass knobs, 52 mm
7.8/10about £16.95
View offer

Mortice pair, then the rim difference

With the numbers matched, take the old knobs off and keep the latch if it still springs cleanly. Slide the new spindle through the follower so an equal length sticks out each side. More Handles asks for that balance, and for pilot holes so the screws do not wander into the latch. A screw that is too long hits the bolt and the knob will not turn. Turn the knob with the door open, then again with it shut. A rim lock uses a different sequence. You measure the backset of the lock case already on the face, and you pass the spindle through that case. One rose is omitted because the lock occupies that side. Sterling’s 45 mm black pair is sold for rim locks and rim sashlocks, not for a latch buried in the edge. If your mortice roses are fixed to the knobs, you cannot discard one and call it a rim set.

When it is stiff or the screws scratch

Two faults show up after the screws are in. The first is a knob that covers the rose, so the screwdriver cannot sit straight. Handlestore and XFORT reviews both describe screws driven at an angle, and the finish marked while you do it. If the rose is inseparable from the knob, you will not get a square drive. Soft or rusty screws are a reason to stop. The second fault is a knob that is too stiff once both sides are on. Disconnecting a spring is a modification, not the recommended fix. If a child or someone with a weak grip cannot turn it, change to a lighter sprung latch or a lever. Stop and call a joiner when the door is certified, when the new lock case has a different footprint, or when the final exit is the leaf you are altering.

Common questions

What do I measure before I drill?
Door thickness, the backset from the edge to the spindle centre, and the size of the square hole in the latch. Confirm a latch or rim lock is already there, and confirm the door is not a fire door. Drill only for screws that match holes you already understand.
How do I know the spindle fits?
It should enter the follower by hand, with an equal length each side. An 8 mm bar is the modern UK size. A bar you have to file, which reviewers report on the mushroom knobs and one Georgian pair, is the wrong fit.
Why do the screws go in at an angle?
On sprung pairs the knob often stays on the rose, so a straight screwdriver cannot reach the screw head. Reviews of the chrome pair and the mushroom pair both describe scratched finishes and angled screws. Pilot holes keep the screw from wandering into the latch.
What backset keeps my knuckles off the frame?
Measure from the door edge to the spindle centre. Trade notes put a practical knob backset around 57 mm, and a longer one is more comfortable. The inch size of the case is not that measurement. Makers differ by a few millimetres.
How is a rim knob different to fit?
The lock case is on the face of the door. The spindle passes through the case, and one rose is left off. You measure that lock’s own backset. A two-rose mortice pair with fixed roses will not sit on it.
When do I stop and call a joiner?
When the door is a fire door, when you are changing the lock on a final exit, or when the new case does not match the old footprint. A like-for-like knob on an ordinary timber latch is the household job. The certified door is not.

Related pages

Best doorknob

Doorknob

Bathroom door knob: privacy without trapping someone

Mortice door knobs: latch, spindle, backset, spring

Mortice or rim door knobs: which pair the door takes

Sources

Public UK and manufacturer 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 these knobs is treated as BS 3621, BS 8621 or Secured by Design.

  1. BSI, BS EN 1906:2012 (retrieved October 2026)
  2. HOPPE UK: BS EN 1906 (retrieved October 2026)
  3. Approved Document M, Volume 2 (retrieved October 2026)
  4. Approved Document Q, 2015 (retrieved October 2026)
  5. Guild of Architectural Ironmongers, accessibility guide (2021) (retrieved October 2026)
  6. Secured by Design: doors, front and back (retrieved October 2026)
  7. More Handles, tubular latch guide (retrieved October 2026)
  8. Suffolk Latch Company: door knobs with locks (retrieved October 2026)