Hi, What are the good ways to measure the True Position or I guess concentricity of pitch diameter / major diameter of an internal 1/4 -28 thread to it's minor diameter? The datum is set to what looks like the major diameter of the ID thread. Is going off the major normal or do most use the pitch diameter? I just scrapped a bunch of parts because I offset a mill/turn lathe's thread mill wrongly. The 1/4-28 was on the face of the sub and I sent the X(center line of the live tool spindle pointing right) *down* 0.010. I meant to send it in the Z 0.010 to scootch in the Min thread call out. And in trying to pull this one out of the fire, we came to realize we have no way of checking the concentricity of PD to to the minor or any other features called out on the center line of the thread. I've got .003 max material positional and the minor is up at the top so it is easily shown - not even argued - the parts are to print. But it aint right and we need to get the checking procedure down. I suggested making the .003 regardless of feature size but that will only make the need to measure stuff just right even more critical. A suggestion was to run the PD to fit those screw-in,ground measury plugs or buy a bag full of graduated measury plugs. But then what to do with tapped holes? We've got the resources to measure pert near any way you folks know of CMM, Laser, String with two knots in it.... Any direction, experiences and help would be much appreciated by me; the guy who just went out in the woods and cut off a long thin willow switch and went back in and handed it to my bosses' boss. And it's not that i don't love you guys the most; but this may show up posted in several other metal head chat groups.