Is that the key to telling? What fins are we looking at here mate? Need to work out how to tell as I don’t want to get the wrong sort. From what I read they’re not interchange, at least not the way I needn’t it to be.
from what i know (which isnt much) i would agree with sparky. 12mm piston will work in both cylinders, 10 mm piston will work only in the original intended cylinder.