Steel wire is still widely ordered "by gauge" on the Moroccan market. It is useful shorthand between people in the trade, but a source of misunderstanding as soon as you change supplier or import. This guide explains what a gauge really is, what the word "galvanised" does and does not guarantee, and how to word an order that leaves no room for interpretation.
What a gauge is — and is not
The Paris gauge (jauge de Paris, JP) is a traditional numbering system for steel wire. Its logic runs against intuition: the higher the number, the thinner the wire. A JP17 is markedly finer than a JP8.
The origin is industrial: the number corresponded to the count of passes through the drawing die. Each pass reduced the diameter, so counting passes amounted to designating a fineness.
And there lies the problem: a gauge is not a standardised unit of measurement. Several gauge systems coexist worldwide — Paris gauge, British BWG, American AWG — and they do not match. Two suppliers can deliver different diameters under the same number without either acting in bad faith.
The rule to remember: order in millimetres. The gauge number may accompany the order as a familiar marker, but it is the diameter in millimetres that must appear on the docket. If in doubt about the correspondence your supplier applies, ask for their table: any wire drawer will share it readily.
What "galvanised" means — and what it leaves unsaid
Galvanising means coating steel with zinc. The protection works through two complementary mechanisms:
- Physical barrier. The zinc isolates the steel from damp air.
- Galvanic protection. Zinc is less noble than iron. In the presence of moisture it corrodes first, protecting the steel even where the coating has been scratched. That is why a cut end of galvanised wire does not rust straight away.
But the word "galvanised" says nothing about the quantity of zinc deposited — and that is what determines service life. A lightly galvanised wire and a heavily galvanised one look alike to the naked eye and may last five years or twenty in the same environment.
Zinc mass is measured in grams per square metre of wire surface. It is this value, not the appearance, that must be specified for durable outdoor use. EN 10244 governs metallic coatings on steel wire and defines zinc mass classes; EN 10218 covers general technical delivery conditions and dimensional tolerances for wire.
Galvanised, bright, annealed: three conditions, three uses
Bright (or black) wire. Drawn, uncoated. Hard and springy, because drawing work-hardens the steel. For indoor use or further processing.
Annealed wire. Furnace-treated after drawing. The treatment relieves internal stresses: the wire becomes soft again and twists by hand without breaking. This is rebar tying wire — you cannot tie bars properly with hard wire, which snaps on the second turn.
Galvanised wire. Zinc-coated. Essential as soon as the wire stays exposed: fencing, mesh, gabions, greenhouse ties, viticulture.
One point often overlooked: on an exposed structure everything must be galvanised, ties included. A galvanised wire fence fixed with black wire degrades at the fixing points within a season — and those are precisely the points that hold it up.
Wording an unambiguous order
A complete wire order comes down to five points:
- Diameter in millimetres (with the gauge number alongside if that is your habit).
- Condition: bright, annealed or galvanised.
- Coating class if galvanised, or failing that the exposure environment — coastal, indoor, industrial — so the supplier can propose the right class.
- Quantity in kilograms, not metres: wire is sold by weight.
- Packaging: coils, spools, desired unit weight. A 50 kg coil is a two-person lift; an 800 kg spool needs equipment.
To convert length into weight, the linear mass of a round wire is calculated as for any steel bar: ز ÷ 162.2 in kg/m, with the diameter in millimetres. A 2 mm wire therefore weighs 0.0247 kg/m, or about 405 metres per 10 kg coil.
Frequently asked questions
What is the Paris gauge (JP)?
It is a traditional numbering system for steel wire in which the number rises as the diameter falls: a JP17 is finer than a JP8. It is not a standardised unit — the conversion to millimetres can vary between suppliers, which is why you should order in millimetres.
Does a higher gauge number mean a thicker wire?
No, the opposite. The higher the gauge number, the finer the wire. This inverted logic comes from the number of passes through the drawing die.
What is the difference between annealed and galvanised wire?
Annealing is a heat treatment that makes the wire soft, for tying reinforcement. Galvanising is a zinc coating that protects against corrosion, for outdoor use. They answer different needs and are not interchangeable.
How do I know whether a galvanised wire will last outdoors?
Appearance tells you nothing: it is the mass of zinc deposited, in grams per square metre, that determines service life. Specify the coating class you need, or describe the exposure environment so the supplier can propose the right class. EN 10244 defines those classes.
How do I convert metres of wire into kilograms?
The linear mass of a round wire is ز ÷ 162.2 kg/m, with the diameter in millimetres. A 2 mm wire weighs 0.0247 kg/m, so a 10 kg coil holds about 405 metres.
The values given in this guide are theoretical benchmarks drawn from the standards cited. They do not replace a structural calculation note, nor the manufacturer's documentation. For any sizing, have your assumptions validated by a design office.
