.6631" Class X Go (Plus) Plug Gage, Class X Tolerance (+.00004"/-.00000"). Certificate Of Accuracy Included. Use As Masters To Calibrate Measuring Equipment Or To Gage Parts Directly. Either Way, These Class X Plug Gages Provide Accurate, Cost Effective Measurement Standards Perfect For Both The Shop Floor Or A Metrology Laboratory. Go (Plus) Or Nogo (Minus) Tolerance .00004”Up To .8250", .00006" For Pins .8251" To 1.0000". Sizes Available Every .0001" Up To 1.0000". 2" Long Tool Steel; 60/65 Hrc, 4 Microinch Finish Or Better, Round Within 1/2 Of Tolerance. Certificate Of Accuracy Included. Vermont Gage Usa Part #141166310