A total newb, I busted the star fangled nut on my new road bike, while trying to tighten the headset. Generally speaking, how does a person know what size star-nut to use?

In my case, a quarter fits snugly inside the steerer tube while resting on the old star-nut, which indicates to me that I need the 1" star nut. Is that correct?


  • 2
    A quarter of what?
    – Vorac
    Commented Oct 14, 2014 at 7:22
  • @Vorac en.wikipedia.org/wiki/Quarter_%28United_States_coin%29 Commented Oct 14, 2014 at 7:52
  • Note that if you did ruin the star nut, you need to either tap the old one further down or drill the old one out before putting in a new one. Also, if you over tightened it, I think when installing the new one you should use the star nut tool.
    – Batman
    Commented Oct 14, 2014 at 12:40
  • Better than a star nut is an expansion nut of the kind that are used with carbon stems. Easier to install and far better repartition of pressure on the stem.
    – Carel
    Commented Oct 14, 2014 at 15:00
  • I didn't know what a Star Nut (or Star Fangled Nut) was until I looked it up. It's a self-expanding (star shaped, of course) nut often used in threadless headsets.
    – Johnny
    Commented Oct 14, 2014 at 17:59

1 Answer 1


Measure the external diameter of the steerer. This should be either 1" (25.4mm) or 1 1/8" (28.6mm).

This is not the sole determinant of star-nut size, as a variety of materials may be used for the steerer tube, each requiring a different wall thickness.

As your internal diameter is at least 24.26mm, this would mean a maximum wall thickness of 0.57mm for a 25.4mm external diameter, which is insufficient even for steel. With a 28.6mm external diameter, the wall thickness would be up to 2.16mm which suggests the steerer is made of some grade of Aluminium alloy.

If you ask your local bike shop for "a star nut for a 1 1/8" alloy steerer", they should be able to supply an item that fits. The star nut will be about 26-27mm in diameter as it needs to embed itself in the steerer wall.

I don't recommend fitting it yourself unless you have the proper tool; It is easy to misalign the nut and bend the tabs.

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