THIS IS THE BEST AND THE MOSY POWERFUL BIG BORE CYLINDER SET FROM CHINA! PBU YELLOW JACKET COPY, 5 PORT CYLINDER, EXTREME POWER RANGE GAINS, NEW BILLET HEAD DESIGN, TWO TRIANGLE WINDOWS PISTON, REPLACEABLE BILLET CAPS, 44mm PLUS ADDITIONAL TRANSFER DESIGN, COMPLETE EXHAUST PORTING, DOME WRIST PIN, BEARING & CIRCLIPS AND COPPER GASKETS INCLUDED. CIRCLE CRANK IS ALL STEEL CONSTRUCTION, MADE BY IN HOUSE CNC MACHINED, VERY NOTICEABLE TORQUE AND TOP END GAINS. *piston is for 10mm pin. If requires 12mm, please let us know in payment note. The 12mm piston has one window only.