I can't seem to find a reasonable priced thread gauge to check pitch diameter on internal threads. (Like 3 wire but internal) I don't trust go/no go because I want a measurement not a "feel". Example: If you were threading a 6" dia. nut and checking with a no go and the middle was looser and out of spec, you wouldn't know how much or if it was in or out of spec. I've heard of doing the ball bearing thing which makes the most sense to me. I just cannot believe nobody has made a reasonably priced tool with exchangeable balls (like wire set sizes) that would do this. I've seen the spring gauges too but really looking for a universal tool that doesn't cost a fortune and does a huge range of threads like a inexpensive set of wires will. Again I'm shocked nobody has done this. Maybe I should patent / manufacture one? I have a couple ideas but can't belive nobody has beat me to it.