ASTM A193 Grade B7 Zinc Flake Coated Bolts

Chrome Moly Alloy Steel

Zinc flake coating for high-strength bolting

Zinc flake systems are non-electrolytically applied coatings made from zinc and aluminium flakes with a binder. They are widely considered where high corrosion resistance, controlled friction and reduced risk of internal hydrogen embrittlement are important. The complete system may include a basecoat and lubricated topcoat.

Standards route

ISO 10683 specifies non-electrolytically applied zinc flake coating systems for steel fasteners. The designation must be paired with project requirements for corrosion performance, colour, friction and temperature because commercial systems are not interchangeable.

Assembly control

A topcoat can provide a defined friction window, but tightening values still need validation for the fastener, nut, washer and joint. Repeated tightening, handling damage and contaminated threads can change performance.

Fit and coverage

Coating thickness must be compatible with thread tolerance and recess geometry. Specify gauging after coating, acceptable touch marks, local repair policy and any masking requirement.

Information to include on the purchase order

ISO 10683 designation or the approved proprietary system.
Required corrosion test duration and acceptance criteria.
Coefficient-of-friction range and test method, when torque control matters.
Colour, topcoat, temperature and chemical exposure requirements.
Batch traceability, thread gauging, adhesion and coating-thickness reports.

Primary reference: ISO 10683:2018 — non-electrolytically applied zinc flake coating systems.