How To Measure And Find Your uPVC / Composite Door Gearbox With Our Finder
uPVC Door Gearbox Finder
The gearbox (also called the centre case) is the heart of a uPVC multipoint door lock — it's what the key and handle operate. When it fails, the door won't lock or won't open. Finding the right replacement comes down to three key measurements: Backset, Overall Width and PZ. Get those three and you'll find your gearbox. Brand and spindle type help narrow it down, but those three measurements are what matter most. Pick what you know below.
Find My Gearbox
Pick at least one filter. The dropdowns only show options we currently stock — counts in brackets tell you how many gearboxes match.
New to this? Start with the parts explained, then follow the measuring guide — or send us a photo and we'll match it for you.
Gearbox Anatomy & The 3 Key Measurements
If you're new to gearboxes, it helps to know what you're looking at before you measure. Here's a standard multipoint centre case with the parts labelled and the three measurements that matter most marked in red.
1
Backset
Door edge to the centre of the cylinder hole.
2
Overall Width
Full width of the whole centre case, end to end.
3
PZ
Centre-to-centre between the spindle hole and cylinder hole.
Get those three right and you'll find a gearbox that fits. The other parts — and the brand — help you narrow things down:
Spindle holes
Where the door handle passes through. A single-spindle gearbox has one; dual and split gearboxes have two (or one split in half).
Euro cylinder hole
Where the euro cylinder — the barrel the key goes into — passes through.
Deadbolt / hook
The bolt or hook that throws out to lock the door when you lift the handle and turn the key.
Latch
The sprung bolt that holds the door closed when it's shut but not yet locked.
Latch snib
Rare, and only on certain centre cases for special handles. It lets the latch be held back (held in) when turned, so the door won't latch shut.
How to Measure Your Gearbox
Steps 1–3 are the three that matter most — Backset, Overall Width and PZ. Nail those and you can filter straight to your gearbox. Steps 4 and 5 (brand and spindle type) help narrow it down further. The easiest way is to remove the existing gearbox first — undo the two faceplate screws and slide it out — but you can also measure in situ if the door still opens.
Step 1
Measure the Backset
The backset is the distance from the edge of the door (the front face of the faceplate) straight in to the centre of the euro cylinder hole.
- Lay the removed gearbox flat with the faceplate facing you
- Measure from the front of the faceplate to the centre of the cylinder hole
- Because you're measuring to the centre of a hole, it's easy to be a millimetre or two out — so always confirm it against the overall width in Step 2
Most common: 35mm on uPVC doors, 45mm on composite doors. Brands like GU also make 30mm and 40mm, which sit close together and are easy to confuse — that's exactly why the overall width cross-check matters.
Step 2
Measure the Overall Width
The overall width is the full width of the whole gearbox centre case, measured end to end — not the narrow faceplate strip.
Why we use this. It isn't an industry-standard spec, but it's the most reliable way to pin down the backset. Backset is measured to the centre of a hole, which is fiddly to get exactly right — and several backsets sit very close together (a GU comes in 30, 35, 40 and 45mm). The overall width is a simple edge-to-edge measurement that's much easier to nail, and each backset pairs with one specific overall width. Measure both and they confirm each other:
| Backset | Overall width | Example |
|---|---|---|
| 30mm | 46mm | GU 30mm |
| 35mm | 51mm | GU / standard uPVC |
| 40mm | 56mm | GU 40mm |
| 45mm | 61mm | composite doors |
If your two readings don't pair up (say you got 35mm backset but 46mm overall width), re-measure — the overall width is usually the one to trust, since it doesn't rely on finding the centre of a hole.
Step 3
Check the PZ
PZ is the centre-to-centre distance between the spindle hole (where the handle sits) and the euro cylinder hole (where the key goes).
- Measure centre to centre, in millimetres
- Almost always 92mm on modern uPVC doors
Most common: 92mm (92pz) on modern gearboxes. Older patio gearboxes can be 70mm; some Avocet ATK gearboxes use 48mm. On a dual-spindle gearbox the second (lower) spindle is usually 62pz — see Step 5.
Step 4
Identify the Brand (nice-to-have)
Finding the brand is a nice-to-have — it points you in the right direction, but it isn't the be-all-and-end-all. Here's why:
- Many of these brands are now the same company. Assa Abloy has bought up a lot of door-hardware makers, so names like Mila, Lockmaster, Paddock and Safeware are often the same gearbox under different badges — and interchangeable.
- So the stamp can mislead. Your strip might say "Mila" when what you actually have is sold as a Lockmaster. Treat the brand as a pointer, not the final word.
- The three measurements are what count. Backset, Overall Width and PZ will find you a gearbox that fits, whatever the badge says.
To find it: check both ends of the faceplate for a stamp, etch, or catalogue number (e.g. "3500-35"). Look for Yale, Fullex, GU, Lockmaster, Mila, Paddock, Safeware, Avocet, Trojan, APECS, Maco, Roto, Saracen, Millenco, Hoppe, ERA, Winkhaus or Fuhr.
Can't find a stamp, or not sure? Don't worry about the brand — get your Backset, Overall Width and PZ, filter with those, and if you're still stuck, email or WhatsApp us a photo and we'll identify it.
Step 5
Identify the Spindle Configuration
The spindle is the square bar the handle slots onto. uPVC and composite doors use one of three arrangements — getting this right matters because dual and split gearboxes need a specific type of handle, and a single-spindle handle won't work on them.
Single Spindle
One spindle hole. A single spindle bar runs through the gearbox and the handle operates the latch from both sides of the door. The most common arrangement on standard uPVC doors. Takes a standard door handle.
Dual Spindle
Two separate spindle holes. The lower spindle (usually 62pz) drives the outside handle, which deliberately does not retract the latch — so you can't get in from outside without using the key first. A common security setup on front doors. Requires a special dual-spindle handle. The most common dual layout is 92pz / 62pz, with the 62pz spindle lower down for the external handle.
Split Spindle
Works like a dual spindle — the outside handle won't retract the latch without the key — but instead of two separate holes it uses a single split spindle (also called a split follower). That's a two-part spindle bar that meets in the centre of the gearbox, letting the inside and outside handles work independently: the inside handle retracts the latch and throws the bolts as normal, while the outside handle stays fixed until the key is used. The key thing to get right here is the spindle — you fit a split spindle (one split in half), not a special handle.
Not sure which you've got? Look at the spindle hole with the handle off: one square hole = single; two holes = dual; one hole with a visible split down the middle = split.
Common Questions
What is the backset on a uPVC door gearbox?
Backset is the distance from the edge of the door to the centre of the euro cylinder hole. 35mm is most common on uPVC doors and 45mm on composite. Because it's measured to the centre of a hole it's easy to mis-read by a millimetre or two, so confirm it against the overall width.
What is the overall width and why do you use it?
It's the full width of the whole gearbox centre case, end to end. It isn't an industry-standard spec, but it's an easy edge-to-edge measurement that pins down the backset — each backset pairs with one overall width (30mm/46mm, 35mm/51mm, 40mm/56mm, 45mm/61mm). If your backset and overall width don't pair up, the overall width is usually the one to trust.
What is PZ on a gearbox?
PZ is the centre-to-centre distance between the spindle hole and the euro cylinder hole. Most modern uPVC gearboxes are 92mm PZ. On a dual-spindle gearbox the lower spindle is usually 62pz.
What's the difference between single, dual and split spindle?
Single spindle has one hole and the handle works the latch from both sides — the standard setup. Dual spindle has two separate holes; the lower one (usually 62pz) drives the outside handle and won't retract the latch without the key, and it takes a dual-spindle handle. Split spindle gives the same security behaviour but uses a single two-part "split" spindle (a split follower) that joins in the middle of the gearbox — so the fix is fitting a split spindle, not a special handle.
What are the spindle holes, cylinder hole, deadbolt and latch snib?
The spindle holes are where the door handle passes through. The euro cylinder hole is where the key cylinder passes through. The deadbolt or hook is what throws out to lock the door. The latch is the sprung bolt that keeps the door shut, and the latch snib — rare, for special handles — lets the latch be held back when turned.
Does the brand need to match exactly?
No — brand is a helpful pointer, not a requirement. Many brands are now the same company (Assa Abloy has acquired a lot of door-hardware makers), so Mila, Lockmaster, Paddock and Safeware are often the same gearbox under different badges and interchange freely. Your strip might even say one name when you actually have another. What matters is matching the three measurements: backset, overall width and PZ.
What if I broke a door handle getting the old gearbox out?
It happens a lot — seized locks often mean you have to apply force, and handles can snap. Every gearbox product page shows a recommendation block with the door handles that physically fit that gearbox, so you can order both at once.
Not sure what gearbox you've got? Send us a photo.
Snap a clear photo of your existing gearbox (faceplate, centre case, spindle holes, and any visible stamps) and we'll identify it and recommend the right replacement.
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Send your photos and measurements to our sales team and we'll reply with the right gearbox.
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