PROX pistons are precision machined on the latest, state of the art CNC equipment. The same low-expansion, low-friction piston alloy is used as is used for all major Japanese engine manufacturers. set of 2 Prox Pistons Kit available in any of the following size for yamaha superjet 1994-2007 All PROX Piston Kits are supplied complete with Piston Rings, Wrist Pin and Circlips, ready to install! available in 81.00 mm. 81.25 mm. 81.50 mm. 81.75 mm. 82.00 mm. 82.50 mm. 83.00 mm.