hi stewart it has a fibre gasket on the base and just standard steel one on top i changed the piston to a wiesco about 25 hrs ago and it had a thicker alloy base gasket on the base i was told that you cant reuse them so just bought a complete gasket kit, the piston i took out had a b on top dont no what that means, bike run sweet just like doing the little bits and pieces that i can manage, not like your killer kx,s the boys at work eyes pop out when i tell them what you can do. cheers.