10mm vs 11mm Castor Stems: Will Replacement Castors Fit Your Chair?

Every week someone emails us the same worried question: “will these fit my chair?” And the answer nearly always comes down to one measurement — the width of the metal pin on your existing castor.

The thirty-second check

Tip your chair over and pull one castor straight out of the base. A firm tug does it — they're held by a friction ring, not a thread. Now look at the metal stem. Measure across it with a ruler or callipers:

11mm — congratulations, you have the universal standard. Nearly every office chair sold in the UK, from budget task chairs to £900 ergonomic thrones, uses an 11mm × 22mm push-fit stem. All Aeten® replacement castors and glides are made to this spec and push straight in.

10mm — you almost certainly own an IKEA chair. IKEA marches to its own drum with a 10mm stem, and an 11mm part will not fit, no matter how optimistically you push. We'd rather tell you now than after checkout.

Why push-fit stems are brilliant

No tools, no thread to strip, no wrong direction to turn. The friction ring on the stem compresses as you push it into the socket and springs back to hold the castor firm. Replacement takes about a minute per castor.

What about threaded stems?

A small number of older or European chairs use threaded stems (usually M8 or M10 bolts). If your castor unscrews rather than pulls out, our push-fit parts won't fit — but email us a photo anyway and we'll point you in the right direction.

Still unsure? Free fit-check

Photograph your castor pin next to a ruler and email it to info@chairoutlet.co.uk. We'll confirm fitment before you order — it's the reason our returns rate is nearly zero. Once you're sure, the soft PU castors (£6.99) or chrome glides (£17.99) are five minutes from transforming your chair.