This is an oversized piston for the Pinasco 215/225 cylinder kit. This is a C size. With aluminum cylinders like this, each cylinder has a stamp on the upper edge. If your cylinder has a 0 the next size up is A. If your cylinder has an A your next size up is a B. If you cylinder has a B your next size up is C. Once you have run a cylinder for a while and it starts to get worn you can upsize to the next piston to tighten the tolerances. For example : If your 0 cylinder is worn and you have already run the A piston in it you can now run the B piston after that.
If you have seized a cylinder and damaged the Nikasil liner than none of that matters because the liner is destroyed and buying an oversize won't fix it. It's a new cylinder or having the liner redone (expensive).
