I found this bolt from my friends bike (from an adjustable stem).

And I need another bolt like this for my second hand bike because it didn't come with it. It would be much appreciated if you can help me with this. Thank you.

The black part on the top is just grease.

enter image description here

  • We need dimensions. The diameter of the thread and the thread pitch to start with (probably in mm)
    – Chris H
    Commented Sep 2, 2017 at 7:34
  • 2
    It's a bolt. With a diameter, length, and thread that can be measured. And no doubt a "head" with an allen recess. Commented Sep 2, 2017 at 12:36
  • 3
    @ChristianLindig politely, avoid hardware store bolts. They tend to be okay for low load situations, but you generally want hardened bolts for high load areas on a bike. So hardware store bolts are totally fine for attaching a fender/mudguard, probably okay for a rack, but definitely not for a child's seat or a stem or a saddle clamp.
    – Criggie
    Commented Sep 3, 2017 at 7:10
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    @Funkollector I'd recommend you take the good bolt along to a LBS and ask for some help. A decent LBS will simply pull one from their parts bin and give it to you for free or for very little cost. Another option is to look around for a bike-cooperative in your city and see what they can do to help you. The part may be free or they may expect a reasonable donation.
    – Criggie
    Commented Sep 3, 2017 at 7:12
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    @Christian the head diameter is too small in relation to the thread diameter to be a standard socket cap head. While I'm more willing than Criggie to use generic hardware (having ridden a few BSOs with obviously rubbish fasteners) I still wouldn't use one where a single point failure would be catastrophic.
    – Chris H
    Commented Sep 3, 2017 at 8:43

1 Answer 1


Looks like any standard M5 or M6 bolt. Go to a hardware store, find a nut that will screw on, and find a new bolt with that nut.

  • 1
    Are you advising that it's safe to use a generic hardware store bolt? Commented Mar 15, 2018 at 9:23
  • @DavidRicherby they are typically made of hardened steel so yes.
    – wski
    Commented Mar 15, 2018 at 14:08

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