I was washing my’12 specialized stumpjumper. When shaking it/drying it off, a screw/bolt came off and I can’t find where it belongs and don’t know what it is. It has threads inside and fits a 3mm Allen key. It’s 6 mm long, about 5 mm wide at the top. I usually do basic maintenance so didnt think I was so clueless but I can’t recognize this item, can someone help me?

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    Do you have any accessories on the bicycle, such as wheel reflectors? If so, are any of the accessories a bit looser than normal? Commented Dec 8, 2022 at 18:26
  • @AndrewMorton's point about accessories is a good one (though IME wheel reflectors tend to use all plastic fittings). Magnets and reed switches for speed/cadence sensors use all sorts of odd fittings of that sort of scale, for example
    – Chris H
    Commented Dec 8, 2022 at 21:24
  • It would help to identify the part if it was in focus.
    – mkrieger1
    Commented Dec 9, 2022 at 0:37
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    A picture of the bike would help. Not even a closeup, but just something to help show a general idea of how it is equipped. (My first thought was blank filler for where the bottle-holder would go, but that would have outer threads, not inner.)
    – MarkHu
    Commented Dec 9, 2022 at 18:52

5 Answers 5


Arghh! got it. thanks for all the input(im the OP)

I looked over everything I thought super closely but ended up test riding and found its the bolt from my dropper lever(old specialized command post). The lever was still working held by the cable and spring but without the bolt, it's loose and could twist off.
I guess the other half of the bolt/nut must have gotten loose and fell off.
thank for all the input and suggestions.

the picture is below, i have a zip tie through where the bolt should go. I guess that will be another question, where can I easily get a part like this? either way glad to have found what was missing.

enter image description here

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    Good to hear! Can you add a picture showing the piece in its correct location?
    – Ted Hohl
    Commented Dec 9, 2022 at 6:29
  • This is called a "chicago bolt" or colloquially a "sex bolt" Probably not the kind of thing you'll find at a big box store, but a specialist fastener hardware shop may have something. Or you might get away with a regular bolt of the right dimensions and thread but it will have an exposed head, that may be okay. It won't be a high-load situation, but do use threadlocker when finally assembling, to stop it falling out again with vibration. Finally - go do an all-over check of fasteners on the bike and see what else might be loose.
    – Criggie
    Commented Dec 11, 2022 at 19:58
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    I'd bet the piece you have left is M3 threading. These M3 bolts/screws come with various heads and the lengths are generally small. If you don't need a head, an M3 "set screw" will be all thread with one end accepting an Allen key. Home, farm or hardware stores with ample selection of bolt bins will have a variety of metric threaded fasteners to choose from.
    – Jeff
    Commented Dec 11, 2022 at 20:12

Could be the "nut" for a bolt mounting a chainring to a spider.

Here's an example of a pair: enter image description here

Perhaps a similar "nut" for one of the rear derailleur jockey wheels.

Perhaps a derailleur hanger attachment "nut"?

Perhaps used in one of the rear suspension pivot points? This seems less likely because of the small size.

Also less likely - something on a brake caliper.

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    At first I though the black at one end was a thread, but zooming in it's not. The proportions look better to me for a jockey wheel than a chainring (too long for the diameter)
    – Chris H
    Commented Dec 8, 2022 at 6:53
  • It looks a bit long for a chainring nut, and those are usually threaded internally and not externally. My guess would be something related to the suspension, but I’m not familiar with MTBs.
    – Weiwen Ng
    Commented Dec 8, 2022 at 13:12
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    5x6mm, with a 3mm allan key is not a chain ring bolt.
    – mattnz
    Commented Dec 8, 2022 at 18:35

I wonder if it's part of a clamp for a brake lever or shifter lever, and has dropped out of the handlebar area.

Pushing/pulling/prodding should show a surprise loose item, and go from there.

Otherwise, start at the front of the bike and methodically look over the whole thing. Much of the bike is symmetrical (other than drivetrain areas) so compare both sides.

If that doesn't help, try actuating brakes and shifters and see what might feel bad/wrong. There's a small risk something else might go sproinging off under spring pressure, which will help identify the area.

Good luck !


My 2 cents is that it is from a clamp of a lock on grip. I have a set of WTB ergonomic grips that have lock on clamps on each end. The notable thing about the clamps is that they are built in to the rubber of the grip. The clamps are enclosed within the grips and secured with a bolt that threads into a long nut that slips inside the rubber of the other side. It looks much like your picture, has internal threads and requires a 3mm Allen key.

Part of a derailleur pulley bolt assembly could be a possibility, although the ones I'm most familiar with (Shimano), are simply a bolt with a shoulder that acts as an axle and threads into one half of the cage. They require a 3mm Allen key.

  • @mw3841 Any solution to where the missing piece went on your bike??
    – Jeff
    Commented Dec 10, 2022 at 16:57

Most likely the chainring bolt. Need exact numbers, and crankset brand/model will definitely help..

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    The OP stated that the bolt takes a 3mm Allen. That is most likely too small for a chainring bolt. I would expect most or all of them to take 5mm Allen keys.
    – Weiwen Ng
    Commented Dec 8, 2022 at 13:12

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