ProX Piston Kits (Sold each). Yamaha RD350/400/RZ350/RD350LC/RD350YPVS (all years). Piston kits include piston, rings, pin and clips. ProX pistons 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. Note: Use of these pistons in air cooled RD350/400 require modification of the piston skirt. We can perform this service for you. You can purchase the piston modification service here on the site under the piston category. Choose piston size, quantity and click add to cart.