Bore gauge
Other places to shop: McMaster-Carr, Manhattan Supply Corp
Starrett, Fowler, Mitutoyo and others
Not to be a downer, just some thing to remember; measuring tools are only as good as the person using them.....it takes practice to be good
Now for the comment that I'll catch heat for...........I wouldn't hold my hand on my *** or get all wound up just because the gauge was graduated in .001 instead of .0001, I can interpolate .0005 on a gauge........plus, you can always change the dial