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My daughter's bike has a threaded headset, and I don't know what tool I need to adjust it. As you can see from the picture, there are the following parts in the stack:

  • a knurled ring, which presumably isn't very tool-friendly
  • a ring (with a diameter of 35 or 36 mm) with three notches spaced equally apart (I'm not sure whether or not this is permanently attached to the knurled ring)
  • a standard six-sided nut, which I assume I can loosen and tighten with an ordinary crescent wrench

It looks like I'll need some sort of special tool for the ring with the three notches. What tool will I need for adjusting this headset?


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I might be wrong but the ring with 3 notches might be just a spacer (not threaded). It that is the case you would need to tighten knurled ring, then six sided nut, and then tighten them against each other – Davorin Ruševljan Jun 18 '13 at 7:01
In the absence of the "Correct tools", I have used plumbers pipe dogs (pipe wrench?) in the past. The large nut needs a pretty large spanner, and as is typically the case, my largest adjustable opens to 1mm too small.... – mattnz Jun 18 '13 at 7:07
Do note that if what you want to do is adjust stem height/angle that's done with the bolt at the top of the stem. And I agree with Davonin that the notched flat thing is probably just a washer, with no threads. You use the knurled nut below it to adjust the bearings, after loosening the top nut. The notches are probably used to prevent the washer from turning (and indirectly turning the knurled nut) while tightening the top nut, but firmly holding the knurled nut will serve the same purpose. – Daniel R Hicks Jul 3 '13 at 15:11
@DanielRHicks I made the adjustments a couple of days ago, and the notched flat thing is threaded (it's not a washer). – amcnabb Jul 4 '13 at 15:06
In that case it's just another lock nut. – Daniel R Hicks Jul 4 '13 at 16:23
up vote 6 down vote accepted

The bottom ring is used to provide tension against the bearings to stop the headset from wobbling around. It only needs to be hand tight, hence no spanner/tool attachments.

The middle and top ring are tightened against each other, as a lock ring to prevent the bottom ring from loosening.

The top ring can be tightened with any spanner of the right size.

The middle ring requires a specialised spanner called a C-Spanner, a hook wrench or a hook spanner. It looks like the image below and is readily available from any bike shop or online store. Eg: Chain reaction sells one from Park tools

enter image description here

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Instead of using special tool for the middle ring you can use simple hammer and chisel (of course use it gently). – J-unior Jun 18 '13 at 7:47
Thanks - I now know what that gadget in my toolbox is for :) – mattnz Jun 18 '13 at 8:50
A quick search isn't revealing products called "C spanner", but I'm seeing a bunch of tools online that look similar to this with names like "lock ring spanner", "shock spanner wrench", "lock ring wrench", and "adjustable pin spanner wrench". Are any of these the same as a C spanner? Are there different sizes of C spanners, or is there just one size? – amcnabb Jun 18 '13 at 15:35
@amcnabb I've updated with some more detail about the hook wrench. The pin spanner is slightly different from what you need. – Mac Jun 19 '13 at 0:03
Thanks for the update. Do spanners work on a wide range of diameters? It looks like bottom brackets are usually around 45mm, but the headset is around 35mm. – amcnabb Jun 19 '13 at 2:55

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