In short. There is no universal centre cap size, and the size of the wheel in inches does not decide it. The car makers' own shops give 56 mm and 65 mm for BMW (by bolt circle, 112 or 120 mm), 66.8 mm and 71.8 mm for Mercedes-Benz, and 66 mm and 71 mm for two classic Porsche wheels; each of them means something slightly different by "diameter", and BMW and Mercedes-Benz both ask for a check by VIN before you buy. To size a cap yourself, measure the recess the cap clips into, not the face of the cap, and note the depth and how it is held. Most caps clip in and come out with a plastic trim tool. No rule in the UK, the US, Canada or Australia makes a centre cap compulsory; UN Regulation 26, which Australia also uses for new models, forbids sharp projections and wing nuts on wheels and hub caps.
What a centre cap is, and what its "size" means
A centre cap (center cap in the US) is the small cover in the middle of an alloy wheel, usually with the car maker's badge. It finishes the wheel and keeps dirt and water off the hub face and the end of the hub. It is not the same part as a wheel cover (a full plastic trim over a steel wheel, called a hubcap in everyday British English), nor a lug nut cover, the small cap over each nut.
Three measurements decide whether a cap fits:
| Measurement | Where you take it | Why it matters |
|---|---|---|
| Recess diameter (clip diameter) | Across the pocket in the wheel face that the cap's clips grip | Decides whether the cap holds; the single figure that must match |
| Face diameter | Across the visible front of the cap | Appearance only; a cap with the right face can still have the wrong clips |
| Depth | From the wheel face to the hub face, and the height of the cap's clips | A cap that is too deep can touch the hub or the end of the axle |
The recess is not the centre bore. The centre bore is the hole that locates the wheel on the hub, and its size is a fitment figure; the cap recess is a pocket cut into the wheel's front face, often larger than the bore, and its size is the wheel maker's choice. Our guide to hub-centric rings and the centre bore explains the bore; this guide is about the pocket in front of it.
The car makers do not all name the same thing. Mercedes-Benz sells caps "for countersink diameter" 66.8 or 71.8 mm, which is the recess in the wheel. Porsche Classic lists a cap for wheels "with an internal diameter of 71 mm", again the wheel. BMW gives the diameter of the cap and its logo, 56 or 65 mm. When a seller's chart gives one number per car without saying which one it is, you cannot tell which of the three you are reading.
Sizes by make, from the makers' own shops
We read the official accessory shops of three makers on 16 October 2026. We kept only figures printed by the car maker itself, with the part number, and left out every reseller's figure.
| Maker and part | Diameter given | What it refers to | In inches | Fits, according to the maker |
|---|---|---|---|---|
| BMW, 36122455268 (stationary cap, small) | 56 mm | Cap and logo | 2.20 | BMW alloy wheels with a 112 mm bolt circle |
| BMW, 36122455269 (stationary cap, large) | 65 mm | Cap and logo | 2.56 | BMW alloy wheels with a 120 mm bolt circle |
| Mercedes-Benz, several references, e.g. A22040001259283 | 71.8 mm | Countersink in the wheel | 2.83 | Selected by VIN |
| Mercedes-Benz, several references, e.g. A16740159009040 | 66.8 mm | Countersink in the wheel | 2.63 | Selected by VIN |
| Porsche Classic, PCG90103810 | 66 mm | Cap | 2.60 | 911 F, 1965 to 1973, and 914, 1970 to 1976 |
| Porsche Classic, SOW91103811 | 71 mm | Internal diameter of the wheel | 2.80 | Fuchs wheels with a 71 mm internal diameter |
Sources: BMW shop, 56 mm and 65 mm; Mercedes-Benz Store Australia, hub caps; Porsche Shop, 66 mm and 71 mm. Inches are our conversion, at 25.4 mm to the inch.
What the table shows:
- The bolt circle, not the wheel size, sets the BMW cap. BMW ties the 56 mm cap to wheels with a 112 mm bolt circle and the 65 mm cap to 120 mm. On the BMW generations our PCD and centre bore by make guide documents, those launched up to 2015 use 5x120 and those launched since 2017 use 5x112, so the year of the car is a first clue, not an answer. BMW still asks you to check by VIN.
- Mercedes-Benz uses two recess sizes, 5 mm apart. The hub caps its Australian shop listed on 16 October 2026 give 66.8 or 71.8 mm in their name, where they give a figure at all, and the product pages we read ask for a check by VIN before purchase.
- Small differences matter. A cap whose clips span 65 mm, in a 66.8 mm recess, would have 0.9 mm of play on each side (our arithmetic, not a measurement): in our reading, enough for the clips to miss their grip.
What we could not source. For Audi and Volkswagen we found no figure printed by the maker. Resellers give 61 mm and also 58 to 59 mm for the same Audi part number, and 65 mm and also 2 1/2 in (63.5 mm) for the same Volkswagen one; we do not publish either. For those makes, measure your wheel or read the part number on the back of the old cap and ask a dealer to check it against your VIN. We do not give a size for any car that its maker has not published.
How to measure your own wheel
- Take the measurement on the wheel, not only on an old cap. If you still have a cap from the same wheel, measure it too: across the outer edge of the clips on the back, and across the face.
- Use a vernier or digital caliper. Hold the jaws level across the widest part of the recess. A ruler gives you a rough figure, and the makers' sizes above differ by as little as 5 mm.
- Measure the depth from the wheel face to the hub face with the caliper's depth rod, then compare with the height of the cap's clips.
- Look at how the old cap was held: plastic clips gripping a lip in the recess, a metal ring, screws from the back, or a cap that is part of a centre-lock nut (on such cars, the cap is not a separate item to change).
- Read the back of the old cap. Look for a part number on the inside; if there is one, it is the fastest route to a dealer check. Our guide to identifying original wheels by style and part number shows where makers print them.
- Check whether the wheel is original. A cap made for one wheel maker's recess rarely suits another's, even on the same car.
Clip-in, screw-in and stationary caps
Most car makers' caps clip in: plastic tabs, sometimes backed by a metal spring ring, grip a lip in the recess. Some aftermarket wheels and multi-piece wheels hold the cap with screws or bolt it to a plate; the wheel maker's fitting sheet says which, and that is the document to follow.
Stationary caps (often sold as floating or self-levelling) keep the badge upright while the wheel turns. BMW sells its own, and its shop lists the limits plainly (our translation): they are not for steel wheels, must not be used with snow chains, and may turn with the wheel for a moment in some driving conditions. BMW recommends having them fitted only by an authorised BMW workshop (BMW). BMW parts dealers add that, by design, a stationary cap stands a few millimetres further out than the standard one, which matters where there is little room.
BMW does not give the reason for the snow chain warning; if you fit chains on any car, read the handbook and the chain maker's instructions first. Our guide to the parts of a wheel shows where the cap sits against the spokes and barrel.
How to remove and refit a centre cap
Tesla publishes the clearest procedure we found, in its service manual for the 2017 to 2023 Model 3 (Tesla service manual):
- Tool. A wheel trim removal tool (Tesla part 1044206-00-A).
- Removal. On wheels with a separate centre cap, insert the tool in the hole in the cap and pull; on the 18 inch "aero" wheel cap, pull the cap with both hands to release its clips.
- Refitting. Position the cap so the bottom of the Tesla "T" points to the valve stem, then press the centre firmly until it snaps into place.
For lug nut covers, Tesla's owner instructions say to pull the cover from behind on cars built from about January 2024, and to use the cover tool (or a small Allen key) in the hole at the base of the "T" on earlier cars; for both, make sure each cover is fully secure before driving (Tesla, lug nut covers; wheel covers).
Other makes follow the same principle, with different tools. A plastic trim tool does not mark the paint the way a screwdriver does; if the cap will not come, look for a slot or a hole before you lever, and check whether it is screwed from the back. After refitting, pull lightly on the cap: if it moves, the clips have not engaged.
If you are removing caps to change a wheel, do that with the car on level ground and the parking brake on, before you raise it. Never put any part of your body under a car held only by a jack: use axle stands. Tighten the wheel nuts to the car maker's torque, as our wheel nut torque guide explains, and see how to change a wheel safely for the full sequence. If a cap was hiding a damaged or missing nut, have the wheel checked before you drive on.
What the rules say, country by country
Europe and the UK. UN Regulation No. 26, on external projections of passenger cars, has a paragraph on wheels. Paragraph 6.7.2 reads: "The wheels, wheel nuts, hub caps and wheel discs shall not exhibit any pointed or sharp projections that extend beyond the external plane of the wheel rim. Wing nuts shall not be allowed." Paragraph 6.7.3 lets wheel discs that cover the wheel and hub nuts stand out beyond the body's outline only if the projecting surface has a radius of curvature of at least 30 mm and the projection never exceeds 30 mm (text published in the EU Official Journal in August 2010, copy on Lexaris). It applies when a new car model is assessed before sale, not to a cap you buy later; in our reading, the same paragraph is still a sensible test for any cap you add.
Great Britain, the MOT. The MOT inspection manual tells the tester, in section 5.2.2: "You must not remove wheel hub caps." The defects listed under 5.2.1 and 5.2.2 concern loose or missing nuts, bolts and studs, fractures, distortion, and a wheel and fixings that are not compatible; there is no item for a missing centre cap (MOT inspection manual, updated 14 October 2026). Outside the test, regulation 100 of the Construction and Use Regulations 1986 requires parts and accessories to be in a condition that causes no danger (legislation.gov.uk); a cap that comes off at speed is a hazard to others.
Australia. Australian Design Rule 92/00, External Projections, registered on 31 October 2018, reproduces the same paragraph 6.7 in its Appendix A (UN R26, 03 series). It applies to new models from 1 July 2019; other vehicles may continue to meet ADR 42/04 instead (ADR 92/00, clause 3).
United States. Federal Motor Vehicle Safety Standard No. 211 used to cover wheel nuts, wheel discs and hub caps. NHTSA proposed rescinding it on 19 June 1995, judging it unnecessarily design-restrictive and saying that remaining safety concerns were better handled by State laws on vehicle use (60 FR 31947). The current Code of Federal Regulations shows section 571.211 as reserved (eCFR): there is no federal standard on centre caps today. Equipment rules for cars in use are set by each State.
Canada. Section 211 of the Motor Vehicle Safety Regulations, the Canadian counterpart, is shown as repealed by SOR/97-421 (Justice Laws, current to 21 September 2026). Provincial inspection rules apply to cars in use; we have not read each province's.
Original caps on aftermarket wheels
A car maker's cap fits an aftermarket wheel only if that wheel's recess was cut for it: same recess diameter, same lip for the clips, enough depth. Some wheel makers offer this, others supply their own cap. Before you buy used wheels, ask which caps come with them, as our buying used alloy wheels checklist suggests, because a set without its caps can be hard to complete.
Wheels from Onyx Forged
Onyx Forged does not recommend a size or an offset, and it does not assume that a car maker's cap will fit a made-to-order wheel. If you want to keep your car's original caps, say so at the start and ask customer service what the recess of your wheel will take; the answer depends on the design, and it is better settled before the wheel is drawn than after it is fitted.
Frequently asked questions
Are wheel centre caps a universal size?
No. The makers' shops we read give 56, 65, 66, 66.8, 71 and 71.8 mm, and the "diameter" sometimes means the cap and sometimes the recess in the wheel. Measure the recess, or check a part number against your VIN.
What size are BMW centre caps?
BMW's shop sells its stationary caps in 56 mm for BMW alloy wheels with a 112 mm bolt circle and 65 mm for a 120 mm bolt circle, and asks for a VIN check. On the BMW generations we have documented, 5x112 arrived with those launched from 2017; the VIN check decides.
What size are Mercedes-Benz centre caps?
The Mercedes-Benz shop sells caps for two countersink diameters in the wheel, 66.8 mm and 71.8 mm, and requires a VIN check before purchase.
Does the wheel size in inches tell me the cap size?
No. BMW ties its cap size to the bolt circle; none of the makers' pages we read gives cap size by wheel diameter.
How do I get a centre cap off?
Use a plastic wheel trim tool in the slot or hole of the cap and pull, as Tesla's service manual describes; check first whether the cap is screwed from the back. Refit by aligning it with the valve and pressing the centre until it clicks.
Will I fail the MOT without centre caps?
The MOT manual has no defect for a missing centre cap, and it tells the tester not to remove hub caps. Missing or loose wheel nuts are a major or dangerous defect.
Are floating centre caps legal?
Nothing we read forbids a cap that stays upright; UN Regulation 26 and ADR 92/00 forbid sharp projections beyond the rim and wing nuts. BMW says its stationary caps are not for steel wheels and must not be used with snow chains.
Can I put original caps on aftermarket wheels?
Only if the wheel's recess was made for them. Ask the wheel maker before you buy.
Where to go next
For the hole behind the cap, read hub-centric rings and the centre bore; for your car's bolt circle, PCD and centre bore by make. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards: design your wheels.
Sources
- BMW official accessory shop: stationary cap 56 mm, 36122455268; stationary cap 65 mm, 36122455269.
- Mercedes-Benz Store Australia: hub caps category; hub cap A22040001259283.
- Porsche Shop: hub cap 66 mm, PCG90103810; hub cap for Fuchs wheels, 71 mm, SOW91103811.
- Tesla: Model 3 service manual, wheel cap; wheel covers; lug nut covers.
- UN Regulation No. 26, paragraph 6.7 (text published in the EU Official Journal, August 2010).
- Australian Design Rule 92/00, External Projections (registered 31 October 2018).
- eCFR, 49 CFR 571.211; Federal Register, 60 FR 31947 (19 June 1995).
- Canada, Motor Vehicle Safety Regulations, C.R.C., c. 1038, section 211.
- GOV.UK, MOT inspection manual, sections 5.2.1 and 5.2.2; Construction and Use Regulations 1986, regulation 100.
All pages were read on 16 October 2026.
The Onyx Forged design office.