Pretty sure its from one of the registerable ones (97+), will probably also fit early~mid 90s RMs too. It was on my '00 RM125 when I got it, but the axle is too small in diameter and too long for the RM.
Rim has one significant flat spot (see second pic, at about the 1 o'clock position), some spokes have minor rust, but otherwise fine. I figure it could be good for a dirt track tyre on an RM, or a road tyre on an RMX. Includes disc, and the axle (if I can find the axle).
$50 + postage.
Nathan.
04000 23847.