Galvanised Steel Strapping Specifications: What to Put in Your RFQ

A specification for galvanised steel strappings is only useful if it is unambiguous to someone who cannot see your project. Most disputes on this product do not come from bad manufacturing — they come from a drawing that could reasonably be read two ways, where the supplier read it the cheap way and the buyer read it the expensive way.

This is a practical specification checklist, written around what the standards actually require.

The three specification families you will meet

Suppliers will quote against whichever family your market uses, and the part can usually be built to any of them:

• ASTM A653 — zinc-coated steel sheet specification reference.
• ASTM D3953 — steel strapping specification.
• ISO 9227 — salt spray for the zinc system.

The mistake is to specify a standard reference without specifying the class or grade within it. If you write only the standard number, the supplier will quote the lowest class that satisfies it. Write the standard and the level you want.

Dimensional data that has to be on the drawing

For this product the critical dimensions are: width 12.7 / 16 / 19 / 25 mm; thickness 0.5–0.9 mm; coil 20–50 kg.

Three rules that prevent most dimensional disputes:

1. Give tolerances on every functional dimension, not just the nominal values. A nominal dimension with no tolerance is legally “as the supplier chooses”.
2. Say which dimensions are functional and which are cosmetic. Suppliers prioritise what you prioritise, and they cannot guess.
3. State the gauge or measuring method where a dimension is critical. Two inspectors with different methods will disagree about the same part.

Material and grade

The base specification is cold-rolled steel strip, hot-dip or electro zinc coated, soft to medium temper. Grades commonly offered include:

• soft annealed (sign fixing, cable fixing)
• medium tensile (general packing)
• heavy zinc coat 275 g/m² (outdoor)
• electro-zinc (indoor, smooth finish)

Ask the supplier to state the grade on the quotation, not on an assumption. Grade substitution is the single most common silent cost reduction, and it is usually invisible in the finished part — a 201 stainless component looks exactly like a 304 one until the second winter.

Surface treatment

The usual finish for this product is spangle or min-spangle zinc; waxed or polymer-lubricated.

Two points worth writing into the order:

• A measured requirement, not a process name. “Hot-dip galvanised” is a process; “70 µm minimum, tested by coating mass on three parts per batch” is a requirement.
• What happens at cut edges and drilled holes, if any. These are where coatings are habitually broken and where corrosion starts.

Type tests and routine tests

These are different things and are frequently confused in quotations:

• Type tests qualify the design once. On this product: zinc coating mass (g/m²) per lot; salt spray 240–480 h by coat class; tensile and yield per ASTM A370.
• Routine tests are run on every batch: coil camber and edge check.

Specify which type-test reports you want supplied as documents, and which routine test results must accompany each shipment. On a first order, ask for the type-test report before you place it.

The failure modes your specification should be closing

• White rust on arrival — coil stored damp or wrapped hot; zinc hydroxide blooms across the face — storage discipline, not zinc weight, is usually the cause
• Strap softening under load — soft temper sold where medium tensile was specified; the strap stretches and the load loosens on the first bounce
• Zinc flaking at the buckle — heavy spangle zinc with no passivation; the coating shears off under the seal and exposes bare steel

Each of these can be turned into one line in the specification. That is the real purpose of writing it out: not bureaucracy, but making the specific failure you are worried about somebody’s explicit responsibility.

A specification skeleton you can reuse

1. Scope: Galvanised Steel Strapping to be supplied as galvanised strapping band, zinc coated steel strap, gi strapping, galvanised packing band.
2. Dimensions and tolerances: width 12.7 / 16 / 19 / 25 mm; thickness 0.5–0.9 mm; coil 20–50 kg.
3. Material: cold-rolled steel strip, hot-dip or electro zinc coated, soft to medium temper; grade soft annealed (sign fixing, cable fixing) or better.
4. Standard: ASTM A653 — zinc-coated steel sheet specification reference; ASTM D3953 — steel strapping specification; ISO 9227 — salt spray for the zinc system.
5. Finish: spangle or min-spangle zinc; waxed or polymer-lubricated.
6. Tests: zinc coating mass (g/m²) per lot; salt spray 240–480 h by coat class; tensile and yield per ASTM A370; coil camber and edge check.
7. Marking and packing: coils paper-wrapped and palletised, edge-protected; outdoor grades film-sealed.
8. Inspection: pre-shipment, against this specification, with photo evidence and test records.

Related: the galvanised steel strapping quality inspection checklist turns this specification into an inspection plan you can hand to a third-party inspector.