CHS is the round sibling of RHS and SHS, made to AS/NZS 1163 in the same C350 grade. Common gate and balustrade sizes are 25, 33.7, 42.4, 48.3, and 60.3 mm outside diameter, in wall thicknesses from 1.6 to 4.0 mm.
CHS turns up most often as handrails (a 33.7 mm OD CHS is the standard handrail diameter for stair balustrades) and as decorative pickets on balcony rails. The round profile is harder to grip than a square section, which is sometimes the point and sometimes a problem.
CAD60 doesn't currently offer a CHS-framed gate model, but CHS shows up in balustrade models as a balustrade top rail or baluster option.