Looking at the pistons for the 924S 2.5L 8V in the PET it shows these three Tolerance Groups 0, 1 and 2, what does that mean this is for the 100mm piston.

tnx
Dan

 

In the realm of accurate machining of precision fit components, there is a tolerance range given for dimensional specifications.
Pistons for a 100mm bore might be 99.985mm plus or minus .01mm. Porsche divides this .03mm range into 3 categories, basically small medium and large.
Porsche does this with the bores as well and upon assembly, they match the tolerance groups of pistons with the equivalent tolerance group for the block so the clearance between piston and bore is more closely controlled. The tolerance group number will be indicated on both the piston head and the block deck.