Fits:1986 - 2002 CR80R (.060 OVER BORE SIZE & will not work on OEM piston) 2003 - 2007 CR85R (.040 OVER BORE SIZE & will not work on OEM piston)1993 - 2001 YZ80 (.060 OVER BORE SIZE)2002 - 2018 YZ85 (.040 OVER BORE SIZE)