The NSR150SP "A" cylinder is the biggest, whereas the "C" piston is the smallest.

This comination will give you 0.05~0.06mm piston/bore clearance. The book spec if 0.04~0.05mm, so in the best case scenario you'll be within spec. The service limit is 0.08mm.

Now, we can only order the "B" piston from Honda. There may be other sizes available from old stock at other outlets, but we order direct, sothat's what we get. Honda told us that this piston can be used with any cylinder and not to worry. Apparently they have discontinued the other sizes.

A "B" piston in an "A" cylinder will give a 0.045~0.055mm clearance. Not a disaster.

My only concern here is that if you fit the "C" piston to the "A" cylinder it may be a little noisy.

On my race 28 we used to run an "A" cylinder with "D" piston for fast tracks (0.047~0.053mm) and a "B" piston for short tracks (0.039~0.045mm). The reason was that at fast tracks the engine could be held flat out for longer and the bigger clearance piston allowed for this with less chance of nipping up. The tighter piston on short tracks was at peak rpm for only a short time so wasn't a problem.