Rice Lake Stainless Steel ASTM Class 4 Precision Metric Test Weight Kit with Screw Knob, 1g Mass Metric, ASTM Class 4 screw-knob style weight for weighing operations Stainless steel construction for stability, resistance to corrosion, and low magnetic susceptibility Meets American Society for Testing and Materials (ASTM) E617, Class 4 specification for use as a reference standard for calibrating semi-analytic balances, and for student use Set includes a precision test weight, handling glove, and protective case