M39.00 x 4.00 6H Steel No-Go Trilock Plug Gage. Vermont Gage USA Part # 302181020. Vermont Gage's Thread Gages inspect the pitch diameter and the functional thread for both internal and external threaded products. All stocked Thread Gages are made to Class X tolerances per ASME B1.2 (Unified Inch screw threads) and ASME B1.16M (Metric M series screw threads). All Thread Gages are supplied with a Certificate of Accuracy. Work Plugs are stocked in 2B & 3B (Inch) or 6H (Metric) classes of fit. Rings and Setting Plugs are stocked in 2A and 3A (Inch) or 6g (Metric) classes of fit. Stocked Work Plugs are chrome plated. All Thread Gages are marked with nominal size, threads per inch (Inch) or pitch (Metric), class of fit and pitch diameters. Nist Traceable, Certificate Of Accuracy Included. Vermont Gage USA Part #302181020