What does "air gauged" mean?

[flabbydan]

I always see manufacturers describing their barrels as being air gauged.  What does that mean?

[KN]

Air gaging is a highly accurate means to measure hole diameters that are being kept to a very tight tolerance. Basically it is a probe designed to allow air to flow around itself. You then measure the amount of air that is escaping and that gives you a diameter for your hole, or in this case the bore size. Hope this makes sense.   KN

[flabbydan]

:-) Thank you!  I think I get the general idea.
Dan