I had some plated down 1mm early on, but they will currently only plate them down .5mm under the current worn out bore. It is bored out, plated then diamond bored. I just get them plated to the max piston size. You are supposed to be able to wear out 5 pistons on the plating. Detonation won't scratch it. I know someone who blew a main bearing with a plated cylinder. There was no damage. He got lucky though in that nothing caught half way through a port. The combustion chamber on his head was trashed. He put in a new one using the same outer shell. He burned up a piston running old gas and had to use acid to get the melted aluminum off. The third piston ran through it was still in it when he sold the machine. Surviving two damaged pistons and still running good on a third, I would think you could wear out more than 5. There was no measurable wear to the cylinder when installing the third piston.