— What is a hollow square for solar?
A solar carport contractor in coastal Queensland prices a 60 m/s site, and the first aluminium-rail quote comes back unusable. The structural engineer rejects the open C-channel twice because it twists under uneven wind uplift. The rail depth cannot clear the six-metre post spacing without a doubler plate. And the palletised aluminium freight quote quietly eats the project margin before a single module is bolted down. The installer replaces a whole hardware family with one rule. A single closed-profile steel member that carries load in both axes. It resists torsion without extra plates, and drills, welds and bolts like a plain post instead of a precision extrusion. That member is the hollow square, more precisely the square hollow section (SHS) steel tube — the same profile listed as square steel tube for solar mounting in our parts catalogue.
Size Details:
A hollow square for solar is a closed square-section steel tube used as the structural backbone of a photovoltaic mounting system. The vertical posts of a ground-mount array, the columns and roof purlins of a solar carport. And the heavy-duty beams of an industrial rooftop rack where an aluminium rail is simply too thin. Top Best Solar factory, wholesale PV racking house) supplies this member as profile SPC-SHS in SD350-ZM steel with a ZAM275 zinc-aluminium-magnesium coating, in sizes from 40×40 mm to 140×140 mm, wall thickness 1.8–3.0 mm, rated to 60 m/s wind load and 1.4 kN/m² snow load, compliant with AS/NZS 1170, DIN 1055, GB50009-2012, IBC 2009, TUV and JIS C 8955:2011, with a 10-year warranty and a 25-year designed lifespan.
But what exactly is a hollow square for solar. Why does a closed square section beat an open channel or a round tube, and how do you specify size, wall thickness and coating for a real ground-mount or carport project? Below is the full breakdown for EPC contractors, ground-mount and carport installers, wholesale PV racking distributors and visitors to topbestsolar.com evaluating a member whose real identity is square hollow section steel tube SD350-ZM ZAM275 40×40 to 140×140 mm 60 m/s 1.4 kN/m² Top Best Solar SPC-SHS, not a thin aluminium rail with a structural sticker.
What a hollow square is, in plain engineering terms
A hollow square is a square hollow section (SHS) — a steel tube with a square outside profile and a continuous closed wall. It formed by cold-rolling a strip of steel and welding the seam, or by a seamless process for heavier walls. In the broader family of hollow structural sections (HSS) it sits alongside the rectangular hollow section (RHS) and the circular hollow section (CHS),the square tube.
Three numbers define the member you buy:
- Profile size (outside dimension). The distance across the square — 40×40 mm, 50×50 mm, 60×60 mm, 80×80 mm, 100×100 mm, 120×120 mm, 140×140 mm.
- Wall thickness. The steel wall, typically 1.8–3.0 mm for solar mounting.
- Grade and coating. Base steel grade (SD350 for SPC-SHS) plus the corrosion coating (ZAM275 here).
Everything else — cut length, punched holes, end caps, welding — is fabrication on top of those three numbers. Our standard stock length is 6 metres, with cut-to-length service to reduce on-site waste.
Hollow square, SHS, SD350-ZM, ZAM275, Top Best Solar
A hollow square for solar is not a thin aluminium rail wearing a structural sticker. It is a square hollow section steel tube — closed, torsionally rigid, symmetrical, easy to fabricate and cheap to ship — carrying the load path of ground mounts, carports and heavy rooftop racks. Top Best Solar supplies it as profile SPC-SHS in SD350-ZM with ZAM275 coating. The size arange from 40×40 to 140×140 mm, 1.8–3.0 mm wall. 60 m/s wind / 1.4 kN/m² snow, compliant with AS/NZS 1170, DIN 1055, GB50009-2012, IBC 2009, TUV and JIS C 8955:2011, backed by a 10-year warranty and a 25-year designed lifespan. Shipped from the same Xiamen factory that builds solar ground mounts, solar carports, Z racking and cable tray systems. Its metric is square steel tube for solar mounting SD350-ZM ZAM275 40×40 to 140×140 mm 60 m/s 1.4 kN/m² Top Best Solar SPC-SHS, not an aluminium rail. See the full specification at solarpartscomponents.com/square-steel-tube-for-solar-mounting.
