I have been seeing a black plastic part on the nuts of the wheels. My bike also has this. I think I have seen this only on old bikes. Does it have a name and purpose?

old bicycle with black nut cover

Some close up:

black plastic nut cover 1 black plastic nut cover 2

  • 1
    Perhaps to be able to unscrew the nuts without having to use a wrench? I'm curious to see some other answers. They also kind of look like the covers that are use when shipping wheels so the axles don't punch through the box but you wouldn't leave those on, and they look a little different. Do you have an up-close picture of them as well?
    – Nate W
    Commented Aug 27, 2018 at 15:27
  • @NateW if they're plastic I wouldn't think they're durable enough to repeatedly unscrew the nut
    – Swifty
    Commented Aug 27, 2018 at 21:53
  • @Swifty a valid point
    – Nate W
    Commented Aug 28, 2018 at 14:54

2 Answers 2


Those look like packing pieces used to stop the axle ends from punching through the cardboard box partially assembled bikes are delivered in.

I'd imaging they are being used to stop the axle nuts getting scuffed or scratched.

  • 1
    That's exactly what they are. They can be removed and discarded, or they can be saved in case the bike needs to be shipped in the future. Commented Aug 27, 2018 at 17:57
  • Packing protections. Some might leave them on as a kind of protection, scratching of objects or cuts from edges.
    – Carel
    Commented Aug 27, 2018 at 17:58
  • Note that some of them replace the quick release skewer so you need to put that skewer back on.
    – RoboKaren
    Commented Aug 27, 2018 at 21:08
  • 1
    I am kind of disappointed by the truth, I was expecting it to be so much more after seeing it on many bikes :)
    – nimcap
    Commented Aug 31, 2018 at 13:22

The flattened black plastic disks are packing covers as the other answer attests. You see these on low-end bikes in a box because ... well.. they come flatpacked in a box.

But some bikes come with decorative nut covers — especially for through-hole, bolted axles. This helps hide the exposed bolt and makes it less likely you’ll scrape your leg against the exposed threads. I see this on ”mom bikes” in Japan where there are hardly any quick releases.

  • 1
    Do you have a close up shot of the decorative type? I’m apprehensive of googling decorative nut covers ;)
    – Swifty
    Commented Aug 31, 2018 at 17:56

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