Industries we serve

Solar Mounting & Racking Hardware

Bolts, nuts, washers and clamp screws for rooftop and ground-mount PV structures — finished against the exposure the designer actually assumed, not against a colour.

A PV array is sold on a 25-year production curve, so every part of the structure inherits a 25-year expectation — including an M8 bolt that costs a few baht. Two facts decide the specification and neither of them is the colour of the passivate: the atmosphere the array sits in, and the fact that the rail it clamps to is almost always aluminium. V.S. Heat Treatment plates and hardens the small carbon-steel hardware of mounting systems in production lots: rail bolts, T-bolts, module clamp screws, rail nuts, roof-foot hardware and the washers that go with them.

Typical specification bands in this sector

Typical specification bands in this sector
Property class	8.8 · ISO 3506 A2-70 / A4-70 where stainless is specified
Hardness	22–32 HRC (class 8.8, ISO 898-1)
Materials	S45C · SCM435 · SWCH10B21 · SUS304
Coating system	Zn + Cr3+ + sealer · hot-dip (ISO 1461) and Zn-flake (ISO 10683) are other suppliers
Coating thickness	8–25 µm Zn (ASTM B633 SC3–SC4) — hot dip is typically 45–85 µm
Salt spray (NSS)	projects ask 480–1,000 h NSS; a sealed electroplated system is normally quoted lower
De-embrittlement bake	only at ≥ 320 HV or class ≥ 10.9 — most racking hardware is 8.8
Inspection methods	ISO 3497 local minimum thickness · ISO 9227 · gauge check after coating

Solar drawings are usually written by a racking designer rather than a fastener engineer, so they tend to state a coating and a class but not an exposure. Tell us the exposure and the numbers below stop being generic.

Standards commonly cited

ISO 898-1 ISO 4042 ISO 2081 ASTM B633 ISO 10683 ISO 9227 ISO 3497 All standards →

Steel grades commonly specified

S45C SCM435 SWCH10B21 SUS304 All steel grades →

How fasteners actually fail here

1Red rust on the hardware long before the modules age

Zinc is consumed at a rate set by the atmosphere, and the corrosivity categories in the ISO 9223 family exist because a rural inland site and a coastal or heavy-industrial site are not the same problem. The arithmetic is unforgiving: an electroplated layer measured in single-digit microns cannot carry the same number of years as a hot-dip layer measured in tens of microns, and no passivate or sealer closes a gap that large. An array in an aggressive atmosphere is therefore either specified with a thicker coating system from a different process, or with stainless, or with a maintenance plan that someone has actually costed.

2The bonding path that deliberately destroys the insulation

Aluminium rails and module frames are usually anodised, and that oxide is an insulator — which is exactly why earthing and bonding hardware is designed with serrations or teeth that bite through it. The joint that satisfies the electrical requirement is therefore a deliberate metal-to-metal contact between aluminium and a plated steel fastener, in the open air, wetted by every rainfall. Whatever the corrosion drawing says, that contact is the place to look first.

3Preload lost in slotted rail connections

Racking uses slotted channels and T-bolts so installers can adjust on site, and the clamping force in that joint depends on friction the torque wrench never measures directly. Wind loading is cyclic uplift rather than a static number, daily thermal movement works the joint, and any soft layer in the stack — a thick coating, a painted rail, a nylon washer — embeds and relaxes. Coating thickness is part of that stack, which is why a thickness range with an upper limit belongs on the drawing.

4The wet crevice nobody inspects

A module clamp traps rainwater between the frame, the clamp and the rail. That pocket stays wet for hours after the exposed surfaces have dried, and zinc in a permanently damp crevice is consumed at a completely different rate from the shank an inspector can reach with a thickness gauge. If the drawing does not say which surface is significant, the measurement will be taken where it is convenient rather than where the part actually corrodes.

Defect guides that matter in this sector

Early red rust on plated fastenersRed rust well before the specified salt-spray hours: thin coating in thread roots and recesses, damaged passivation, handling damage and test-plan mismatches, with the checks that find the real cause.White rust on zinc-plated partsWhite powdery zinc corrosion in storage and transit: passivation, drying, sealer and packaging faults that cause it, and how to judge it against a salt-spray acceptance criterion.Poor phosphate adhesion — coating rubs off, paint liftsPhosphate that wipes off, coarse powdery crystals and paint peeling from a phosphated fastener: cleaning, activation, bath control and post-treatment causes, with the practical checks that identify each.Thread gauge failure after platingWhy plated screws stop accepting the GO gauge: coating thickness lands in the thread allowance. How ISO 4042, ISO 965-1 and ISO 1502 handle it, and what to specify before production.

All defect guides →

Documentation a buyer in this sector should receive

The corrosivity category the designer assumed, written on the drawing or the purchase order. It is the single most useful line a solar buyer can give a finisher, and it is almost always missing.
A coating thickness report stating minimum LOCAL thickness with the method and the measurement position, and the classification if the project names one — an ASTM B633 service condition or an ISO 2081 designation carries a thickness, the phrase "zinc plated" does not.
Where the specification names salt-spray hours, a report to ISO 9227 / ASTM B117 stating the criterion, the interval and the significant surfaces — read alongside the corrosivity category, because chamber hours are a process comparison and the category is what the structure actually stands in.
A plain statement of the process actually applied — electroplated zinc with a trivalent passivate and, where ordered, a sealer — so that nobody downstream in an EPC document pack reads it as hot-dip galvanizing.
Traceability from each delivered box back to the plating run, which on a staged solar delivery is what lets one call-off be held while the rest of the array is built out.
Every report carries job and lot identity, the material and agreed specification, the test position, method and instrument, the measured values against the acceptance limits, and the date, inspector and approval. We operate under ISO 9001:2015 and hold no solar-specific or EPC-specific approval; no coating report is a 25-year warranty and we will not write one that pretends to be.

What to send us for an accurate quote

1Where the array is: inland farmland, an urban rooftop, a coastal site, or next to heavy industry. Distance to the sea if you know it.
2The design life quoted for the structure, and whether the fastener is expected to last it or is accepted as a maintenance item.
3The coating classification the project specification names, or a thickness range with both a minimum and a maximum.
4What the fastener clamps to: bare or anodised aluminium rail, galvanised purlin, stainless clamp, painted steel — and whether the joint is also an electrical bonding point.
5Property class or grade, and whether the parts are carbon steel for us to plate or stainless you are supplying (we do not plate, pickle or passivate stainless).
6Quantity per call-off and how it is shipped: racking hardware is usually delivered in stages against an installation programme, and it sits on site before it is fitted, so packing and the documents the EPC needs at handover both belong in the enquiry.

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Recommended services

Zinc Plating Cr3+Heat Treatment Testing Laboratory

Common parts we finish

Bolts Nuts Washers Screws Anchor Bolts All part types →

Questions buyers in this sector ask

Electroplated zinc or hot-dip galvanizing for a solar farm?+

For a structure expected to stand outdoors for decades in an aggressive atmosphere, thickness is the whole argument, and hot-dip puts down a far heavier layer than electroplating can. We run electroplated zinc with a trivalent passivate and an optional sealer; we do not hot-dip, and we will say so rather than take the order. Electroplated hardware is a sound choice for sheltered, roof-mounted or lower-exposure positions and where the specification sets a service condition our process meets. Send the project specification and the site, and we will tell you honestly which side of that line your part sits on.

The rails are aluminium. Does that change what I should ask for?+

Yes, in two ways. A steel fastener in contact with aluminium is a bimetallic pair in the open air, and the fastener is usually the smaller member; and if that same joint is also the earthing or bonding path, its design intentionally breaks through the anodised layer to make metal-to-metal contact. Tell us which joints are bonding points, what the mating part is, and whether isolation washers are used, because it changes what thickness and which finish system is worth paying for.

Do you supply A2 or A4 stainless solar hardware?+

We are a heat-treatment and plating subcontractor, not a fastener stockist, and stainless is not zinc plated — if the specification calls for stainless to ISO 3506 classes, that is a material decision made when the hardware is bought. We do not pickle or passivate stainless either. What our lab can do for stainless parts you already have is measure hardness, examine a microsection and run a salt-spray comparison.

The bands on this page are typical industry values, not a guarantee for any specific part. The governing drawing, customer specification and standard always take precedence, and every value is confirmed against your part before production. V.S. Heat Treatment operates under ISO 9001:2015; no other certification or sector approval is claimed.