well thats why i do not care much for them coating i feel its better to know were the piston stops and the coating starts i feel the same and even more so with crank .rod bearing s they give you a bore size to finsh the block to your should not size the bore to the piston coated skirt the HARLEY SCREAMING EAGLE PISTON S have a spot were there no coating so you can mic the REAL piston and set size . other do not and like i said your taking there word on the real size were i have put them in but bit bigger 0005 so if they want 001 piston to wall i bump them out to 001.5 race stuff its not a big deal were .001 more or less may not hurt were you can be at 003 to 008 piston to wall if coating there fine if wears off thats fine .but if the bore is to small then the coating go to come off just as fast . i do not under stand what you saying about the rings ? the bore s if not prep good is what i mean is the bore bottom of bore edge breaking this so you do not shave the piston s as there moving farther down the bores and skirts can come out of bores