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Zinc Coating – Mil-Spec: QQ-Z-325B


Class 1 .0010”
Class 2 .00050”
Class 3 .00020”
Type 1 Without supplementary treatments.
Type 2 With supplementary chromate treatment.
Type 3 With supplementary phosphate treatment.

ASTM Designation: B 633

Electrodeposited Coatings of Zinc on Iron and Steel.

Type Description

As-plated without supplementary treatment
With colored chromate conversion coatings
With colorless chromate conversion coatings
With phosphate conversion coatings

Thickness Classes for Coatings:

Classification* Number and Conversion CoatingSuffix Service Condition**Thickness, Min µm

Fe/Zn 5
SC 4 (very severe)
Fe/Zn 12
SC 3 (severe)
Fe/Zn 8
SC 2 (moderate)
Fe/Zn 5
SC 1 (mild)

* Iron or steel with zinc electroplate. Numeral indicates thickness in micrometres.

** Where service conditions are valid only for coatings with chromate conversion coating. Type II for SC 4 and SC 3 and Type III for SC 2 and SC 1.

Corrosion Resistance Requirements:

TypesTest Period, h



Examples of appropriate service conditions and description of service conditions

SC 4 – Very Severe: Exposure to harsh conditions, or subject to frequent exposure to moisture, cleaners, and saline solutions, plus likely damage by denting, scratching, or abrasive wear. Examples are: plumbing fixtures, pole line hardware.

SC 3 – Severe: Exposure to condensation, perspiration, infrequent wetting by rain, and cleaners. Examples are: tubular furniture, insect screens, window fittings, builder’s hardware, military hardware, washing machine parts, bicycle parts.

SC 2 – Moderate: Exposure mostly to dry indoor atmospheres but subject to occasional condensation, wear, or abrasion. Examples are: tools, zippers, pull shelves, machine parts.

SC 1 – Mild: Exposure to indoor atmospheres with rare condensation and subject to minimum wear or abrasion. Examples are: button, wire goods, fasteners.


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