THESE ARE STOCK TYPE OVERSIZE REPLACEMENT PISTON KITS INCLUDES PISTON, RING SET, PISTON PIN AND 2 CLIPS YOU WILL NEED TO HAVE YOUR CYLINDER BORED IF IT IS NOT ALREADY THESE WILL FIT ALL YEARS OF ATC90 CT90 ST90 CL90 S90 SL90 CM91 50.75MM_317P 51.00MM_317Q 51.50MM_317R OSPK90OLDPICK_YOUR_SIZE_HERE: 50.25MM_S141850.50MM_S141950.75MM_317P51.00MM_317Q51.50MM_317R52.00MM_317S