It is nothing more fancy than an M8 bolt on the XTZ. I can't say how long it is (without taking one off!), but the length is kind of irrelevant, assuming whatever bolt you fit is long enough not to fall out when the axle is slid back to its rearmost position. The swingarm is hollow, therefore the bolt thread can go in as far as you like, so the longer the better - you can always trim some off if necessary.

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