We used to knurl the piston skirt on standard pistons on cars when using oversized rings , to keep the piston from rocking. if you have to much gap between your piston and cylinder wall the piston will rock back and forth cutting a crescent in the cylinder wall with the rings. I had that happen on a Harley Shovelhead that I bought from a friend with a brand new bore job & rings in it, 50 miles after the build I had to tear it down and take it back th the shop that did the bore job, he looked at it and asked "what a mess, who did that bore job" should have seen him squirm when it handed him his receipt, wanted to just redo the bore job and me buy the new pistons, NOT!