X is short for Xtreme. Since there are too many extreme's or xtremes out there, they just shortened it. It's just a coincidence that it happens to be the Roman numeral 10 and they are on the level 10 bolt.
x-mag, x-valve are all short for xtreme.
x-mag, x-valve are all short for xtreme.


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If it was, it would be the X-Frame, not the Y.

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