UK size guide for wheel nut covers and bolt caps. Bolt covers in Car Accessories are cosmetic plastic caps for wheel nuts, sold in packs of 20, in 17 mm, 19 mm and 21 mm. A cover does not remove a locking wheel bolt, and it does not replace a lost locking key.
Covers vs locking keys
A wheel nut cover is a plastic cap for the hex of a wheel nut or wheel bolt. It changes the look of the fastener. It is not a tool, and it is not a lock.
- Bolt cover / wheel nut cover - Cosmetic plastic cap, sold in packs of 20 in Car Accessories. Sized by the hex: 17 mm, 19 mm or 21 mm.
- Locking wheel bolt or locking wheel nut - The security fastener already on the wheel. It needs its own removal key. A plastic cap does not unscrew it.
- Locking key (anti-theft key) - The socket that matches that security head. If it is lost, you need a matched key, not a coloured cap.
Listings name Audi, VW, BMW and Mercedes, and describe the caps as universal for that hex size. That means the cap is chosen by the measurement across the flats, not by a key pattern. They are not sold as a keyed lock.
Lost the removal key? Use the locking wheel bolts and anti-theft keys guide, then look in anti-theft bolts. A cover from Car Accessories will not remove the locking wheel bolt and will not replace the key.
What a cover does
A bolt cover is a push-on plastic cap. It hides the hex and changes the colour. That is the whole job.
- It does not clamp the wheel.
- It does not hold the nut on.
- It does not replace a lost locking key.
A pack of 20 covers one car, with spares.
If a cap is tight, a separate alloy removal tool is sold for 17 mm, 19 mm and 21 mm caps. The tool is not an anti-theft key.
How to measure across the flats
To choose what size wheel nut covers to order, measure the existing nut across the flats with a spanner or a caliper. Across the flats is the distance from one flat side of the hex to the opposite flat side. The sizes on the site are 17 mm, 19 mm and 21 mm.
- Try a 17 mm, 19 mm or 21 mm spanner on the nut you want to cover. The spanner that fits snugly is the cover size.
- Or measure the same distance with a caliper, flat to flat, and match 17 mm, 19 mm or 21 mm.
- Ignore the thread size. M12 or M14 describes the bolt thread, not the hex the cap has to fit.
- Check all four corners if the nuts have been replaced. One axle can differ from another on some cars.
17 mm, 19 mm and 21 mm
Shoppers often search 17mm wheel nut covers, 19mm wheel bolt caps, or 21mm locking nut covers. Those names all refer to the hex size across the flats. Each one is still a cosmetic plastic cap, sold in a pack of 20.
| Hex size | Listing name | What it is |
|---|---|---|
| 17 mm | 17mm wheel nut covers | Cosmetic cap for a nut that measures 17 mm across the flats. Not an M12 or M14 thread size, and not a locking key. |
| 19 mm | 19mm wheel bolt caps | Cosmetic cap for a 19 mm hex. Wheel nut covers and wheel bolt caps are the same type of cap; the hex measurement is what matters. |
| 21 mm | 21mm locking nut covers | Cosmetic cap for a 21 mm hex. The words “locking nut” in the listing name do not mean the cap unlocks or removes a locking wheel bolt. |
Audi, VW, BMW and Mercedes appear on the listings because the caps are offered for those marques. The description is universal for that hex size: a 19 mm cap fits a 19 mm hex, whether or not the badge on the car matches the title. It is still not a keyed lock.
Colour is cosmetic
Colour does not change the size. Measure 17 mm, 19 mm or 21 mm first, then pick a finish. Finish is cosmetic and must be chosen after the hex size.
| Finish | Cap | What to know |
|---|---|---|
| Blue | Ordinary open-hex cap | Cosmetic finish for a standard hex. Choose it only after the size is settled. |
| Matt black | Ordinary open-hex cap | Cosmetic finish for a standard hex. A different colour will not change the fit. |
| Gold | Ordinary open-hex cap | Cosmetic finish for a standard hex. Choose it only after the size is settled. |
| Grey | Ordinary open-hex cap, and a locking-bolt cap | The ordinary grey cap covers an open hex. The grey locking-bolt cap is a different shell, currently listed in 17 mm. |
| Gloss black | Locking-bolt cap | A different shell from the ordinary open-hex caps. Currently listed in 17 mm. It is still only a cosmetic cover. |
Gloss black and grey locking-bolt caps are a different shell from the ordinary open-hex caps.
Matt black and gloss black are the same hex size when the listing says 17 mm, 19 mm or 21 mm. A different colour will not make a 17 mm cap fit a 19 mm nut.
Locking nuts
A locking wheel nut is often a different shape from the other nuts on the same wheel. It may not take the same cap. Even when a cap sits on it, the cover does not unlock it and does not remove it.
Standard bolts and nuts have an open hex. The usual cap for that hex is 17 mm, 19 mm or 21 mm. Ordinary caps are blue, matt black, gold and grey.
Locking bolts have a shaped security head, not that open hex. The shop also sells locking-bolt caps. Gloss black and grey are listed as locking bolt caps, currently in 17 mm. A locking-bolt cap is still only a cosmetic cover for that shaped head. It does not remove the locking bolt.
Important: wheel nut covers do not remove a locking wheel bolt, and they do not replace a lost locking key. If the key is missing, a pack of caps will leave the locking fastener where it is.
If the locking key is lost, you need the locking wheel bolts and anti-theft keys guide and a matched key or bolt set from anti-theft bolts. Order that, not a cap.
- The standard nuts can take 17 mm, 19 mm or 21 mm covers once you have measured them.
- The locking nut on the same wheel may be a different shape, so the same cap may not fit it.
- Removing that locking nut still needs the correct anti-theft key. The plastic cover plays no part in that.
Ordering from Automotive Outlet
- Measure across the flats on the nuts you want to cover: 17 mm, 19 mm or 21 mm.
- Check all four corners if any nuts have been replaced. One axle can differ from the other.
- Look at the locking wheel nut separately. It is often a different shape and may not take the same cap. The cover will not remove it.
- Choose a colour (blue, matt black, gold, grey or gloss black) only after the hex size is settled. Covers are sold in packs of 20.
- Browse Car Accessories and match the listing to the hex size. Titles that name Audi, VW, BMW or Mercedes are described as universal for that hex size, not as a keyed lock.
If the job is a missing locking key, leave the caps and use the locking wheel bolts and anti-theft keys guide with anti-theft bolts.
FAQ
- What does a wheel nut cover actually do?
- It is a push-on plastic cap that hides the hex and changes the colour. It does not clamp the wheel, hold the nut on, or replace a lost locking key. A pack of 20 covers one car, with spares. If a cap is tight, a separate alloy removal tool is sold for 17 mm, 19 mm and 21 mm caps. That tool is not an anti-theft key.
- Will a cover remove a locking wheel bolt?
- No. A wheel nut cover is a cosmetic plastic cap. It does not unlock, unscrew, or remove a locking wheel bolt. If the locking key is lost, use the locking wheel bolts and anti-theft keys guide and order a matched key or bolt set. Do not buy a cap instead.
- What size wheel nut covers do I need?
- Measure across the flats of the existing nut with a spanner or a caliper. The sizes on the site are 17 mm, 19 mm and 21 mm. That measurement is the hex size, not the bolt thread.
- Are 19mm wheel bolt caps the same as an M14 bolt?
- No. 19 mm is the distance across the flats of the hex. M12 and M14 describe the thread. Order the hex size you measured.
- Do 21mm locking nut covers replace a lost locking key?
- No. The 21 mm listing is a cosmetic cap for a 21 mm hex. It is not a keyed lock, and it does not stand in for a missing removal key.
- Can the front nuts be a different size from the rear?
- Yes. One axle can differ from another on some cars. If the nuts have been replaced, check all four corners before you order one size for the whole car.
- Will a locking wheel nut take the same cap as the other nuts?
- Often no. A locking wheel nut is frequently a different shape and may not take the same cap. The cover still will not unlock it or remove it.
- Is a locking bolt cap the same as a standard bolt cover?
- No. The locking head is a different shape, so use the locking-bolt cap listing. Neither one removes the bolt.
- Does colour change the fit?
- No. Blue, matt black, gold, grey and gloss black are cosmetic. Choose the colour after you have measured 17 mm, 19 mm or 21 mm across the flats.
- Are the Audi, VW, BMW and Mercedes covers a keyed lock?
- No. Those listings are cosmetic plastic caps, sold in packs of 20, and described as universal for that hex size. They are not a locking key.
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