This is the NIST-certified version of REED's 5-step steel calibration block for ultrasonic thickness gauges, built to the same 1018-steel, dual inch/metric-marked five-step design (0.100 through 0.500 in). It comes with a traceable NIST calibration certificate documenting full measurement data and uncertainties, making it suitable for quality programs that require certified reference standards. A carrying case and one-year warranty are included.