Hot-Dip Galvanizing (HDG)

Hot-dip galvanizing is a corrosion-protection process where steel fasteners or parts are cleaned, fluxed, and then dipped into molten zinc to form a tightly bonded zinc-iron alloy layer with an outer zinc coating. This creates a much thicker coating than typical zinc plating and is designed for long-term protection in outdoor and industrial environments. Hot-dip galvanized fasteners are commonly used in structural steel connections, utility hardware, guardrails, and other applications exposed to weather, moisture, and corrosion.

Because the coating is thicker, hot-dip galvanizing can affect thread fit and assembly. Galvanized bolts and nuts are typically made to compatible thread allowances, and galvanized nuts are often tapped oversize to accommodate the coating and allow proper tightening. The coating offers excellent durability and sacrificial protection, but it can be rougher in appearance than electroplated finishes and is not ideal where tight dimensional tolerances or smooth cosmetic finishes are required. Hot-dip galvanizing is usually specified by standards (such as ASTM requirements) that define coating thickness and performance for the intended service conditions.