Aluminum Square Tube 6061, Aluminum, 6061, T6, Square, 4 ft Overall Length, 3 1/2 in Outside Width, 3 1/2 in Outside Height, 0.25 in Wall Thickness, Fabrication Extruded, Mechanical Finish Mill, Yield Strength 40,000 psi, Tensile Strength 45,000 psi, 95 Brinell Hardness, B60 Rockwell Hardness, Includes Material Certificate Yes, Standards ASTM B221, System of Measurement Inch