Hot-dip galvanized square & rectangular hollow section (SHS/RHS) is manufactured by ERW cold rolled steel strip, then fully hot-dip galvanized at 460℃ after pickling & flux treatment. Uniform zinc-alloy coating covers inner wall, outer surface, welds and corners to provide long-lasting anti-rust protection via sacrificial anode effect. Hollow square section features outstanding bending & torsion resistance, no secondary anti-rust painting required, suitable for indoor, outdoor and coastal humid environments. Supports cutting, punching, bending and welding processing. Full sizes in stock, MTC mill test certificate & SGS salt spray test reports available for global export orders, widely used in PV, construction, agriculture, fencing and machinery frames.