The "No Go" Ring" Gage checks one thread element only-the pitch diameter.
The Minor diameter and the Major diameter are cleared beyond those of the "Go" Ring Gage.
Thus the "Go" Ring Gage, in going on the part, insures that the lead and form are correct, and the size is smaller than the maximum permitted pitch diameter
of the part.
The "No Go" Gage, in refusing to go on the part, insures that the size is larger than the minimum permitted pitch diameter.