The new model piston came out mid 2010 as it was a new cast from the factory.

In the new cast they improved

Concentricity of roundness pt dia

Gudgeon holding stays

Front lip angle and thickness

Piston top thickness

Gudgeon hole chmpfer is for ease of removing andnreplacing the g clips. When you put in new g clips you place the elbow of the clip into the groove and push inward. Then to check its seated you turn it back wit a bit of prssure from a flat blade.

Hope this info helps

Oh ps

Forgot the piston maerial alloy was changed to a about 10 higer silicone content. This aids in the malleability of the cast. Ie lessesns the chances of pistons cracking.

Cheers m