Prox Racing Parts (01.2429.B 94.96mm 4-Stroke Piston Kit Fits: Yamaha YZ 450 F 2003-2009, WR 450 F 2003-2013; Gas Gas EC 450 F 2013 Ready to install, ProX Piston Kits are supplied complete with piston rings, wrist pin, and circlips ProX pistons are precision machined on the latest, state of the art CNC equipment and use the same low-expansion, low-friction piston alloy all major Japanese engine manufacturers use Uses an OEM style tin coating to assist the break-in process when you first start your machine Notes: 94.96mm bore, standard compression 12.5:1, forged piston