Also, pin gauges come in plus (+) and minus (-) sizes, be sure to get the minus (-) or they won't fit in the throats.
Actually, they come with a plus or minus tolerance. Most commercial pin gage sets come with either a +0002 or a -.0002 tolerance. That said, having used, and checked hundreds of them over the years, I don't think I've ever found a commercial pin gage that was anywhere near .0001 off either side of the nominal. You can only come within a thou of determining throat size with them anyway. All you know for sure is this one goes in, but the next bigger one doesn't.
Handier than plug gages are taper gages, you just put them in the hole and take a direct reading. They're somewhat spendy, though, for a hobbyist with a limited number of hole sizes to ever have to check.
If you really want to go all out, another option is internal micrometers, but the cost there is a little the other side of nuts.