Why are hot-dip galvanized bolts the most common?

Hot-dip galvanized (HDG) bolts are the most common type of corrosion-protected bolt for one overarching reason: they offer the best balance of high corrosion resistance, durability, and cost-effectiveness for a wide range of applications.

Superior Corrosion Protection is the primary reason. The hot-dip process creates a robust, multi-layered coating that is metallurgically bonded to the steel bolt.

The zinc coating is significantly thicker (typically 50-100 µm or more) than what is achieved with electroplating (e.g., zinc-plated bolts, which are typically 5-25 µm). More zinc means more sacrificial material to protect the underlying steel.

Zinc is more electrochemically active than steel. This means if the coating is scratched or damaged, the surrounding zinc will sacrificially corrode to protect the exposed steel, preventing rust from forming. This is a huge advantage over barrier-only coatings like paint.

The hot-dip process creates a coating that is integral to the bolt itself. The outer layer of pure zinc and the inner layers of zinc-iron alloys are extremely hard and durable.

They can withstand rough handling, shipping, and installation without the coating being easily chipped or scratched off, which is a common issue with thinner electroplated coatings.

During the galvanizing process, the bolt is fully immersed in molten zinc.

This ensures complete coverage, including threads, the underside of the head, and any recesses. This is a critical advantage over methods like spray galvanizing, which can miss hidden areas and lead to premature failure.

While not the cheapest option (that would be plain or zinc-plated bolts), HDG bolts provide the most protection per dollar for demanding environments.

Long Lifecycle: Their long service life (20 to 50+ years in many atmospheres) drastically reduces maintenance, repair, and replacement costs over the lifespan of a structure.

They are vastly more affordable than stainless steel bolts for applications where stainless's specific properties (e.g., non-magnetic, high chemical resistance) are not required.