So i did a little search last night, i send a email to wossner USA, and thanks to them they respond me (not like wossner germany). They tell me that the reference 8547DA is for 94.95 mm piston, listing for KTM SX-EXC520 '00-02 / SX-EXC525 R '03-07 / Betamotor RR525 '05-09. But they dont have listing for ktm/Polaris 525 atv on the wossner catalog. So i check on ktm parts catalog, and prox catalog, and this bikes share all the same piston, so normally there's no problem using it. Now for the reference 8637DA, this is for the high comp 12.50:1 94.95 mm piston.