This machinist tool is an easy to use App to find the Major, Pitch, Minor diameters with Tolerance and Allowance of a metric thread. No need for a trig calculator or expensive book. It works for both internal and external threads Class 6H, 6g and 4g6g. Mostly used in machine shops and by engineers to find the diameters for a specific thread. This app only uses Metric measurement, not Unified.