• ...I don't have any reason to doubt this...
    I do.

    "...even if I managed to get the right sized headset...": what like this?

    "...I would need a special machine to assemble it...": what like this? And WTF does "properly seal it" mean?

    OK, I've made some assumptions (1" threaded fork/ISO thread, which it's likely you would have with a 531 frame), but even if you're using threadless forks or have Italian or JIS threading it's all standardized stuff.

    Have a look at this cribsheet (scroll down for headsets).

    Let us know what frame and forks you're using.

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