Thanks Guys, I think I've got it now.

Tyga's Honda OEM Top End Kits include a Piston - No Mark. This corresponds to Barrel type B.

If this barrel & piston matching is to do with machining tolerances, its very important to match these up correctly, could it not lead to premature seizure?

In general engineering applications, being out of a tolerance band can lead to galling / pick-up of precision machined component surfaces when mating them together.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30