Scooterotica

I've just bought a second hand TS1 225 kit and am checking the piston to bore clearance as per Stickys manual. When I put the feeler guage down the side of the piston I need to go up to a 0.2mm (8 thou near as) until the piston will lift. Am I right in thinking that this gives me a 4 thou piston to bore clearance because the clearance opposite the feeler guage is zero or is the piston to bore clearance actually 8 thou?
Next question is what does grade A, B and C relate to in TS1 piston sizes? I'm going to have to replace the piston because the engine has been run weakand the piston is dimpled. The piston measures 69.8mm diameter on my vernier which with the 0.2mm makes the bore 70mm
All advice gratefully received

To be right get it measured professionally,it will also show if the cylinder has bellied in the bore. Piston grades as quoted in the T5 section of the Haynes Vespa manual show the higher the letter the larger the piston ie C larger than A. As Guilardoni make the T5 top end I would expect the sizes to be something similar with the TS1 kit.

Just pick up the phone to A.F. .. they are quite helpful .. it is correct to say that the grade 'A' is is the first piston size available for standard TS1 kit.