ASTM A153

Covers — hot-dip galvanized coatings on small iron and steel hardware and fasteners (bolts, nuts, washers, threaded items, and small castings/forgings) that are typically centrifuged after dipping, with coating classes by part type.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Fabricated structural steel galvanized after fabrication → ASTM A123.
• The fastener base material/strength → ASTM A307 / A325, etc.
• Mechanically/electro-deposited zinc → ASTM B695 / B633.

A153 covers small centrifuged hardware; A123 covers larger fabricated pieces.

A153 sets minimum requirements for hardware galvanizing:

• Coating Class — minimum coating weight/thickness by hardware class (A–D).
• Centrifuging — spinning to clear threads and cavities of excess zinc.
• Thread Fit — nuts tapped oversize (after galvanizing) to accommodate coating build.
• Adherence & Inspection — coating adhesion and thickness verification.

ASTM A153 is the hardware counterpart to A123, covering hot-dip galvanizing of small parts such as bolts, nuts, and washers. These are galvanized and then centrifuged to spin excess zinc out of the threads, and coating requirements are set by hardware class.

A practical consequence: galvanizing adds thickness, so nuts are tapped oversize after galvanizing to still thread onto the coated bolt. Matching galvanized fasteners to galvanized structural steel (A123) keeps the whole assembly protected.

Engineering Note: Order galvanized nuts specifically for galvanized bolts — a standard nut will not thread onto an A153 galvanized bolt because the zinc build interferes; the oversize-tapped nut is the correct match.