Square Hollow Steel Sections are commonly used in welded steel frames where members experience loading in multiple directions and have very efficient shapes for this multiple-axis loading as they have uniform geometry along two or more cross-sectional axes, and thus uniform strength characteristics.

This makes them good choices for columns. They also have excellent resistance to torsion.

The flat square surfaces of rectangular HSS can ease construction, and they are sometimes preferred for architectural aesthetics in exposed structures. 

HSS is also available in mild steel, such as A500 grade B.