piston/ ring question

[thrownchain]

Got a call from a friend of mine today, he was installing new 56 mm piston set up in his cylinder. He couldn't get even get close to the required end gap. I had him squeeze the ring together and then measure the diameter, he came up with 55.5 mm ring diam, with the piston at 56 mm. Any thoughts on why this might happen?

[viclioce]

Wrong rings for that piston, or wrong oversize set, one that's for a smaller oversize than the piston/bore? Sounds like someone grabbed a mismarked set of rings? Victor