A simple round cylinder gauge measuring tool can be used on both stems, seat tubes and other round tubes to determine inside diameter and roundness. Nice part is there pretty full proof and somewhat affordable you can get nice cheap bicycle one for $25 or so or spend $40 or so for a nice machine grade one. I thin there worth the investment will save a tone of time and hassle figuring out tube hole sizes.
https://www.ebay.com/itm/20210145895...IAAOSw7iZeLVtE