Zinc Wire Packaging Specification: Spool, Coil or Drum, and Why It Decides Your Container
Updated 9 September 2026 · 10 min read · Pack density and container figures are our own calculations
Short answer
Pack format is not a finishing detail - it is a logistics decision that reaches your freight bill and your gun uptime. Zinc wire in 250 kg drums packs at roughly 1,130 kg/m³ and fills a 20 ft container to its weight limit at about 26 tonnes. The same wire on 20 kg spools packs at roughly 590 kg/m³, becomes volume-limited, and will only get about 18 tonnes into a 20 ft container. Choose drums for continuous work and spools for intermittent work, and check the pay-off before you commit to either.
- Formats: 15–18 kg spool, 25 kg coil, 50–250 kg drum
- Coarse wire drives pack size: 3.175 mm normally ships in 250 kg drums, 4.0 mm in 200 kg
- A 26 t order is 104 drums or about 1,300 spools - that is 3.5 hours versus 43 hours of handling
- Specify the moisture barrier and the splice rule. Those two clauses cause the disputes.
The three formats, and what each is actually for
The temptation is to pick by price per kilogram, and drum will win that comparison every time. But the correct question is how the wire leaves the pack, because that is where the cost is actually incurred.
Pay-off is the whole game
A spool has flanges and rotates on a fixed axis. The wire leaves tangentially and the geometry is stable, which is why spools are forgiving. A drum-packed coil has no flanges: the wire is pulled up from the centre of a stationary coil, and if the winding pattern is wrong the wire lifts several turns at once and forms a loop that tightens into a knot. That knot travels down the conduit and stops the gun.
Pack density, and why it changes your container
Here is the calculation that most buyers never see. It is simple but it decides whether you ship in a 20 ft or a 40 ft container, and therefore what your freight costs per tonne.
Deriving effective pack density
Drum pack, 250 kg: assume drum 560 mm OD x 900 mm high volume = pi * 0.28^2 * 0.90 = 0.2215 m3 density = 250 / 0.2215 = 1,129 kg/m3 Spool in carton, 20 kg: assume carton 340 x 340 x 250 mm = 0.0289 m3 density = 20 / 0.0289 = 692 kg/m3 allow 85 % for pallet + stowage loss = 588 kg/m3 Container, 20 ft: usable ~30 m3, payload ~26 t Container, 40 ft: usable ~60 m3, payload ~26 t Drums 26 t / 1,129 = 23.0 m3 -> fits 20 ft WEIGHT limited Spools 26 t / 588 = 44.2 m3 -> needs 40 ft VOLUME limited Spools 30 m3 x 588 = 17.6 t -> max in a 20 ft
| Pack format | kg/m³ | 26 t occupies | Fits 20 ft? | Max in 20 ft | Packs per 26 t |
|---|---|---|---|---|---|
| 250 kg drum | 1,129 | 23.0 m³ | Yes | ~26 t | 104 |
| 50 kg drum | ~900 | 28.9 m³ | Yes, tight | ~26 t | 520 |
| 25 kg coil, cartoned | ~640 | 40.6 m³ | No | ~19 t | 1,040 |
| 20 kg spool, cartoned | ~588 | 44.2 m³ | No | ~18 t | 1,300 |
Read the right-hand column as labour, not just freight. A 26 tonne order is 104 drums or roughly 1,300 spools. At two minutes of handling per pack, receiving and moving that order is about 3.5 hours against about 43 hours. That cost never appears in the wire price and always appears in your operating budget.
Copy this packaging clause
PACKING : ____ (spool / coil / drum), nominal net weight ____ kg per pack
tolerance on net weight +/- ____ %
LENGTH : continuous length per pack required: yes / no
SPLICE : splices or welds permitted: yes / no
if yes, max ____ per pack, to be dressed flush and flagged
WIND : wound for centre pay-off (drum) / flange pay-off (spool)
no kinks, loops, cross-overs or trapped ends
INNER : moisture barrier - vapour-phase inhibitor or sealed PE liner,
desiccant ____ g per pack
OUTER : carton / wooden case / drum, suitable for export
PALLET : ____ packs per pallet, stretch-wrapped,
timber heat-treated to ISPM 15 with mark visible
MARKING : per pack - product, ASTM B833-20, base metal designation,
diameter, net weight, heat/lot number, supplier,
country of origin
DOCS : packing list showing pack count, net and gross weights,
pallet count, and container number
Two lines do most of the work. INNER - the moisture barrier - is what stands between your wire and the condensation that forms inside a container crossing an equator or a cold front. SPLICE is the clause that decides who pays when a spool runs out mid-job: ASTM B833 permits splices provided they do not interfere with the equipment, so if you need weld-free continuous length you have to ask for it.
What we will not tell you
We will not give you a freight rate. Ocean freight on this lane has moved enough during 2026 that any figure we print would be wrong within weeks, and it would be wrong differently for every origin and destination pair. Ask your forwarder for a rate against packs-per-container, which is the number that actually drives the cost per tonne.
We will also not tell you that one format is right for everyone. A jobbing shop spraying gates three days a month should not buy 250 kg drums to save USD 60 a tonne, because the drum will sit open and the wire will oxidise. Buy the pack you will empty, not the pack that is cheapest.
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✔Match the pack to consumption rate, not to unit price
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✔Trial one drum of drum pack on your own conduit before committing
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✔Get packs per container in writing before you compare freight
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✔Specify the moisture barrier and the splice rule explicitly
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✔Check ISPM 15 marking on timber before it reaches the port
FAQ
What packaging options are available for thermal spray zinc wire?
Three main formats. Spools or reels of about 15 to 18 kg, sometimes 20 kg, wound on a flange reel for direct mounting on the spray unit. Coils or bundles of roughly 25 kg, usually strapped and either boxed or drum-packed. And drums holding 50 to 250 kg, with the largest drums used for coarse wire - 250 kg for 3.175 mm and 200 kg for 4.0 mm. Outer packing is carton or wooden case depending on format and destination.
Should I buy zinc wire on spools or in drums?
Spools if your gun mounts a reel directly and your consumption is intermittent, because you gain fast changeovers and simpler handling at the machine. Drums if you run continuously and feed through a pay-off. The deciding factor is pay-off behaviour, not price: drum pack must unwind without kinking, and a badly wound drum will stop your gun more often than a spool ever will. Trial one drum before you commit.
How much zinc wire fits in a 20ft container?
It depends entirely on pack format, and this is the most misunderstood number in the trade. Drum-packed wire runs at roughly 1,130 kg per cubic metre, so a 26 tonne load occupies about 23 m³ and fits a 20 ft container comfortably - you are weight-limited. Spool-packed wire in cartons runs at roughly 590 kg/m³ once pallet and stowage voids are allowed, so 26 tonnes would need about 44 m³ and will not fit; a 20 ft container maxes out near 18 tonnes.
Why does drum-packed zinc wire usually cost less per tonne?
Three reasons that compound. Winding 250 kg onto one drum takes a fraction of the handling that winding 1,300 separate 20 kg spools takes. Packaging material cost per kilogram is lower. And freight is lower because drum-packed wire fills a 20 ft container to its weight limit, whereas spool-packed wire becomes volume-limited and may need a 40 ft container for the same tonnage.
What should a zinc wire packaging clause say?
Name the pack format and net weight, the tolerance on net weight, whether continuous length per pack is required, whether splices are permitted, the inner protection against moisture, the outer packing, the pallet treatment if timber is used, and the marking on each pack. The two clauses most often omitted are the moisture barrier and the splice permission - and those are the two that generate disputes.
How many packs do I have to handle for a 26 tonne order?
About 104 drums at 250 kg, or roughly 1,300 spools at 20 kg. At two minutes of handling per pack that is about 3.5 hours against about 43 hours. The difference rarely shows up in the unit price and always shows up in labour and forklift hours at your receiving dock.
The rest of this zinc wire series
- Zinc Wire Price Trend: September 2026 - what the pack is worth in metal terms before you negotiate the format
- Zinc Wire Market Outlook 2026 - why lead times on drums and spools move with the market
- Zinc Wire Applications - pay-off behaviour: which format feeds which gun without stopping the job
- Zinc Wire Quotation Reference - how to word the pack clause so a damage claim is actually payable
- Zinc Wire Warehousing and Storage - what happens to the pack after it lands, and the dew point rule
Related on this site
- High Purity Zinc Wire - the product page, with the grades we actually stock
- The Complete Zinc Wire Manufacturing Process
Not sure which pack format suits your line?
Tell us your gun type, monthly tonnage and whether you run continuously or in bursts. We will recommend a format, quote packs per container, and send a single drum or spool to trial before you order a container load.
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✔Spools, coils and drums, 15 kg to 250 kg
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✔Packs per container confirmed in writing
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✔Moisture barrier and splice terms to your clause
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✔One sample pack to trial on your own equipment
Useful to include: whether your gun takes a reel or feeds from a pay-off, and the conduit length from pack to gun - it changes how forgiving the winding has to be.
Sources and known gaps
Pack formats and net weights (15–18 kg spool, 25 kg coil or bundle, 50–200 kg and 250 kg drum; 250 kg for 3.175 mm and 200 kg for 4.0 mm; carton or wooden case outer), diameter range 1.3 to 4.0 mm, 99.995% nominal composition: multiple Chinese supplier product listings. ASTM B833-20 clause permitting splices or welds provided they do not interfere with the thermal spray equipment, and the requirement that wire uncoil readily: ASTM International. ISPM 15 requirement for heat-treated timber packaging is a phytosanitary rule that applies to most export lanes; confirm the current requirement with your forwarder.
Derived on this page, with assumptions stated: the drum and spool pack densities of 1,129 and 588 kg/m³, the 23.0 and 44.2 m³ container occupancy figures, the ~18 tonne maximum for spools in a 20 ft container, the 104 versus 1,300 pack counts, and the 3.5 versus 43 hour handling comparison. All depend on the drum, carton and pallet dimensions we assumed. Ask for real dimensions and rerun.
Gaps we did not paper over: we have not quoted any freight rate, because lane rates moved materially during 2026 and any figure would be stale. We have no measured bulk density from an actual shipment - the figures are geometric estimates from assumed pack dimensions. Container payload limits vary by carrier, route and equipment; 26 t is a typical figure, not a guarantee.