The Z-number on a galvanized steel specification is the total zinc coating weight in grams per square meter, counted on both surfaces. It is the single most important variable in how long the product survives outdoors.

What the numbers mean

• Z120: about 17 microns total, indoor or painted-over applications.
• Z275: the standard commercial coating, roughly 40 microns, the default for construction.
• Z600: heavy coating for permanent outdoor exposure such as farm buildings and fencing in coastal areas.

Service life in practice

In a rural inland environment, Z275 galvanized panel typically shows first rust after 15-20 years. In coastal or industrial air with chlorides and sulfides, the same panel may need repainting within 8-10 years, which is where Z450-Z600 or a paint system earns its cost.

Common mistakes buyers make

• Specifying coating below the standard: Z120 roofing will fail early even if the base steel is good.
• Comparing price without coating weight: a Z120 coil can be 8-10 percent cheaper than Z275 and still be a bad deal.
• Ignoring spangle and passivation: chromated or oiled finishes prevent white rust during ocean shipment.

Our supply range

We supply DX51D+Z, DX52D+Z and SGCC coils from 0.3 to 3.0 mm with coating weights from Z120 to Z600, slit to width or cut to length. Every coil ships with coating weight verified on the mill test certificate.

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