Galvanized nuts

A zinc-plated nut is a hexagonal carbon steel nut with a protective zinc coating. It is the most common option for plumbing, heating and general construction applications. Its price is close to that of an uncoated steel nut, while its service life under normal humidity conditions ranges from 5 to 15 years. The coating is available in a matt silver finish or with iridescent passivation.

The category includes nuts manufactured to GOST 5915-70 and their international equivalent, DIN 934. Available sizes range from M4 to M30. Products are supplied in accordance with GOST 5915-70 and DIN 934.

Electroplating and hot-dip galvanizing: understanding the difference

Electroplating produces a thin zinc layer with a thickness of 6–12 μm. The thread retains its nominal accuracy, allowing this type of zinc-plated nut to fit an electroplated zinc bolt without additional adjustment. Its service life ranges from 5 to 15 years in heating, cold-water and hot-water systems, utility basements, heat substations and boiler rooms. It is a versatile option used for most flange connections and steel structures installed in heated indoor areas.

Hot-dip galvanizing involves immersing the component in molten zinc and produces a coating 50–80 μm thick. After hot-dip galvanizing, the nut’s thread fitting diameter increases. For this reason, these nuts are manufactured with an enlarged internal diameter and may only be used with hot-dip galvanized bolts.

An electroplated zinc bolt will fit too loosely in a hot-dip galvanized nut, which may cause the connection to become unstable. A hot-dip galvanized bolt will either not fit into an electroplated nut or will damage the thread. This is the first compatibility issue to check when ordering fasteners for outdoor structures.

Where zinc coating is not sufficient

Zinc deteriorates in environments containing chlorine, including swimming pools and water-treatment systems. It is also unsuitable for contact with food, detergents, acids, alkalis and seawater. AISI 304 or AISI 316 stainless steel nuts should be used in these conditions.

There is no need to pay extra for zinc coating when selecting fasteners for concealed indoor connections or assemblies that will be painted. Uncoated steel nuts are suitable for these applications.

The property class of a zinc-plated nut must correspond to the property class of the bolt. A class 5 nut should be used with a class 5.8 bolt, while a class 8 nut should be used with a class 8.8 bolt. General selection guidelines are available in the “Nuts” section.