ORIGINAL: pe reivers

What I fail to see explained here, Ralph scratched the surface of it, is the system behind the A,B,C.... markings.
To continue from where Aussiesteve left off:
Once in production, after all those many operations, the operator is satisfied with roundness and taper he stops working on the bore. The next station is a hydraulic measuring device that defines the true mean dimension of the bore at height specified in specs. Dependine on that dimension, the cylinder is marked.
Same with piston dimensions. rather than working to the EXACT dimension, which is nearly impossible regarding tool wear and operator intervention, the piston when done is measured. According to measurement it is ''classed'' to match the class of the cylinder sizes.
There you have it in a nutshell. Minimal production costs, and accuracy that competes with multiple cost production systems.
BTW,
MVVS, my favorite manufacurer, does not use this system. Any Cylinder will fit ANY piston in their gas engines (costly, costly). They have to learn a bit still.