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I need to replace my 1" threaded headset, but to my surprise the replacement headset is available for either 30.0mm or 30.2mm inner head tube diameter. Is it possible to tell which one I need without removing the headset cups?

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  • If you currently have a 1" threaded headset then a proposed replacement for "either 30.0mm or 30.2mm inner steerer tube diameter" has incorrect dimensions. 1"=25.4mm. A 30mm dimension is involved with a system that uses an 1⅛" (28.58mm) O.D. steer tube where, at the crown race seat of the steer tube, the dimension is said to be 30mm. This also is the given dimension of the INNER diameter of the crown race for a fork having a straight 1⅛" steer tube. Actual dimensions in these areas differ by hundredths of a mm to allow for the interference fit of the crown race to fork steer tube.
    – Jeff
    Feb 17, 2021 at 4:13
  • @jeff You are right, it looks like I'm a little confused about inner and outer diameters of steerer tubes, headset cups and crown race seats. Still trying to figure that out. However, when looking at Sheldon's cheat sheet you can see that 30.2mm is the most common dimension for 1" threaded headset cups.
    – user430
    Feb 17, 2021 at 10:04

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Probably not.

Knowing the manufacturer of your bike gives a clue but not always definitive.

One is the Italian size and more common. The other is Japanese.

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  • It's a Raleigh made around 1989. I guess it uses 30.2 headset cups because, as you say, it's the most common. But I can't say for sure..
    – user430
    Feb 17, 2021 at 10:31
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    @user430 It becomes more complicated with Raleigh as certain bikes had Raleigh's own standards, with a different thread on the fork and non standard cups. Sheldon Brown has a page about it.
    – Noise
    Feb 17, 2021 at 11:31

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