A500 shapes and HSS sections

A500 covers round, square, rectangular, and special structural tubular shapes, produced within a periphery of 88 in. [2235 mm] or less and wall thickness of 1.000 in. [25.4 mm] or less. In North American practice these products are collectively called hollow structural sections: HSS designations such as HSS6×6×1/4 (square), HSS8×4×1/4 (rectangular), and HSS6.625×0.280 (round) usually refer to A500 material unless the drawing says otherwise.

Rounds resist torsion and look the same from every direction; squares simplify symmetric connection detailing; rectangles put material where a dominant bending axis needs it. Special shapes exist in the specification but are producer-negotiated products.

An HSS designation states nominal outside dimensions and nominal wall. For design, AISC practice applies a reduced design wall thickness to A500 product (commonly 0.93 times nominal for ERW sections) to account for the mass tolerance in the specification — one of the practical differences that ASTM A1085 was later written to eliminate. Your section-property tables should state which assumption they use.

When ordering, specify the shape, outside dimensions, and nominal wall from the standard's dimensional system, and do not mix pipe (NPS) designations with HSS designations on the same line item.

Choose the shape from the load path and the connection, not from habit. Torsion and multi-axis bending favor rounds; simple welded moment connections between members of similar width favor squares and rectangles; architectural exposure often decides the question independently of structural efficiency.

• Rounds: torsion, axial compression, appearance from all angles
• Squares: symmetric detailing, columns, balanced two-axis bending
• Rectangles: dominant single-axis bending, beam applications
• Availability differs by shape and region — confirm before finalizing sizes

Cold-formed square and rectangular HSS have rounded corners whose outside radius depends on wall thickness and producer tooling. This matters for weld fit-up, for fitting cover plates, and for weight estimation: sharp-corner geometric approximations (including this site's calculator) slightly overstate the weight of shaped sections. Section-property tables published by AISC and the Steel Tube Institute account for corner radii.