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I want to convert from 1 inch threaded fork to 1 inch threadless.

What measurements do I need to take into consideration when choosing the fork and headset for my head tube?

Can I fit any headset to steering column / head tube as long as it is threadless and same diameter?

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  • The head tube will be designed for a certain type of headset seat. Most common for a 1 inch era mountain bike will probably be for headset "external cups" which are press fit into the ends of the head tube. Why do you want to switch from 1 inch threaded to 1 inch threadless? My impression is that many more forks are available as either 1 inch threaded or 1 1/8 inch threadless than for 1 inch threadless.
    – Armand
    Commented Jul 20, 2021 at 1:11
  • @Armand I just started building a bicycle from old parts for fun and wanted to change the stem. How can I confirm whether my head tube is compatible with a headset? So any fork would work?
    – fabda01
    Commented Jul 20, 2021 at 1:15
  • The lower bearing might be too short, see bicycles.stackexchange.com/q/52546/9215 for details. Commented Jul 20, 2021 at 15:07

2 Answers 2

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You have the right idea. You can do this freely as long as the new headset is the right cup size for the head tube. The crown race ID of the new headset also has to be correct for the new fork, but 1" threadless forks and headsets use the 26.4mm ID size almost universally (maybe actually universally but there's always an oddball somewhere).

1" threadless headsets are typically all the 30.2mm cup OD size, known in their day as Professional/Campagnolo/ISO and named as EC30 in SHIS. So, most of the time what that means is you can do it freely as long as the headtube is the 30mm ID that EC30 uses. The catch to be on the lookout for with what you are doing is that there are other 1" sizes that use a different size headtube bore. The most populous one of these is JIS, which is 29.8mm. If the frame is JIS (EC29 in SHIS) you can have it machined by a shop to be EC30. JIS is common enough that you need to confirm it's not JIS. There are some other 1" sizes where it can't be made to work, but they are all far less common.

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  • Thank you for answer. Let me see if I got it right. Headsets are typically EC30 in SHIS, but head tubes are typically JIS (EC29 in SHIS). Supposing my head tube is JIS (EC29 in SHIS), in order to be able to fit the headset into my head tube I either convert my head tube to EC30 in SHIS or get a JIS (EC29 in SHIS) headset? As for the fork / crown race compatibility, most likely to be compatible diameter.
    – fabda01
    Commented Jul 20, 2021 at 8:02
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    @fabda01 JIS is very common in some eras and locales of 1" headtube bikes, so it's just good practice to check that it's not JIS unless you know it's not. The question of which is most common is bigger and hard to measure, but JIS is common enough that you just need to look out for it, especially on 70s and 80s bikes not made in Europe or the US. Other than that yes you have it. Commented Jul 20, 2021 at 15:08
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The industry has developed a standard system listing the key measurements and information for headsets. Park Tool has a good description here: https://www.parktool.com/blog/repair-help/standardized-headset-identification-system

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