Centre distance (CC) is the measurement between the two fixing points a device or cover frame screws into — and it’s the single dimension most likely to make or break compatibility between a box and the device system you’re pairing it with. Two boxes can look identical and still use different centre distances. Across our range, 60 mm is the dominant centre distance for standard single-position boxes, while 67 mm and 70–71 mm show up specifically on junction/connection boxes and the Concrete & Precast Boxes series — and the right one depends entirely on the device or cover-frame system in your project, not on which box looks closest to what you already have.
Why centre distance matters more than most other dimensions
Outer diameter and depth affect whether a box physically fits into the wall. Centre distance affects whether the device you’re installing can actually be screwed into it. Get the outer diameter and depth right but the centre distance wrong, and the box goes into the wall perfectly — and then the cover plate or device won’t seat, because the screws don’t line up with the fixing lugs. It’s a smaller-looking number than outer diameter, and it causes a larger share of on-site problems.
Where centre distance comes from
Centre distance is set by the device or cover-frame system, not by the box manufacturer in isolation — a box is designed to match a specific device system’s established fixing centres, which is why the same nominal “size” of box can carry different centre distances depending on which market and which device convention it was built for.
The pattern across our range
| Centre distance (CC) | Where it’s used | Example models |
|---|---|---|
| 60 mm | The dominant fixing centre for standard single-position hollow-wall/timber boxes and their matching switches, sockets and covers. | ETM610S, ETM680S, ETM750S, ETM761S, ETM850S |
| 67 mm | Used for certain junction/connection boxes and larger single-position devices where the device itself needs a wider fixing base. | ETM613S, ETM931S, ETM835S |
| 70–71 mm | The Concrete & Precast Boxes series’ own convention, and the “gang distance” used when two standard boxes are connected side by side. | ETM834S (70 mm); precast ganging distance (71 mm) |
| 84 mm | Double-gang cover plates spanning two ganged boxes. | Double-gang cover plates across several series |
See the model comparison page for the current, live centre-distance data by model.
What happens when centre distance doesn’t match
If the centre distance is even a few millimetres off, the device or cover frame’s fixing screws won’t align with the box’s lugs. In the best case, this is caught before installation and the box is swapped. In the worse case, it’s caught on site, after the box is already set into the wall or cast into a concrete element — at which point the fix is expensive and, in precast work, sometimes not possible without replacing the element.
A checklist for confirming centre distance before you order
- Measure the centre distance on the actual device or cover frame you intend to install, not on a box you assume matches it.
- If replacing an existing box, measure the existing box’s centre distance directly rather than relying on its model name or apparent size.
- Cross-check the centre distance against the model’s published specification, and treat an unpublished field as “unconfirmed,” not “probably standard.”
- If your project spans multiple device systems (for example, different markets on the same build), confirm centre distance separately for each.
- When in doubt, send the device/cover-frame reference for a fit check before ordering — this is exactly what a market-fit review is for.
What we do differently
We publish centre distance per model as it’s confirmed, rather than defaulting to a single “standard” figure across the range — because there isn’t one, and implying there is would set a buyer up for exactly the mismatch this article is about. Where a model’s centre distance isn’t yet published on the model page, we say so rather than approximating it.