i was told NOT to do this
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here is what you should have to put on a new sprocket. the 2 top rings are original parts, the bottom is a shim i made. whatever you buy determines the thickness of the shim you need. i bought a shim washer, made the middle bigger and slotted the outside for the nuts with a dremel.

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when you take off the wheel, you only need to lift the entire sprocket configuration out of the hub. you do not have to loosen the nuts first to
take it off. the whole thing will slide right out. so never mind the new
hub first. park it first and rip it down. if you can get a spacer in there,
that may be all you need. but do it now.! good luck. dont give up.
just do what the other guy who sold it to you didnt do.
congrats on df250rtb ownership. the bike is the balls.