I have a 2000 exc 250 and the part number stamped on the cylinder is 546.30.205.000. The pats fiche as my manual has part number 546.30.205.044 listed for a 2000 EXC 250. I'm doing a top end right now and have the vertex B piston kit and the ring gap is measuring .5mm. The tolerance is supposed to be .3-.4mm. I do remember the guy I bought it from mentioning something about possible an SX cylinder or head but didn't pay much attention at the time as he wasn't very knowledgable about the bike or mechanically inclined. He always had the shop do the work. I know that the vertex B kit for the SX uses different rings than the EXC kit and that's why I'm trying to figure out which cylinder I have. Thanks!