Made from AISI 1144 Steel with HRC 20-25 Heat Treat Compatible with Olympic bars, curl bars, tricep bars & dumbbell bars. Includes a 12mm Hex Allen Wrench for installation. Olympic bars have a specialized hex bolt at the end of the bar, integral to keeping the weights in-place. Please verify your specific size, thread and pitch. Highest Quality Aftermarket Parts Available 100% Satisfaction Guaranteed