ProX Piston Ring Sets (ea) Yamaha RD350/400/RZ350/RD350LC/RD350YPVS (all years). Piston replacement ring sets for ProX pistons (sold each - enough for one piston). ProX pistons ring sets are manufactured in Japan and are designed to meet or exceed OEM specifications. Available sizes are 64.0mm,64.25mm,64.50mm,64.75mm,65.0mm,65.25mm,65.5mm. Click add to cart and choose size.