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Steel nuts

A steel nut is a hexagonal nut made of uncoated carbon steel. It is the basic and most affordable option for use with a bolt. These nuts are intended for dry indoor environments, concealed connections inside valves and equipment, and assemblies that are painted or primed immediately after installation.

This category includes standard-accuracy hex nuts manufactured to GOST 5915-70, as well as their international equivalent, DIN 934. Available sizes range from M6 to M30, with property classes 5 and 8. Products are supplied in accordance with GOST 5915-70.

Where to Use and Where Not to Use

Uncoated carbon steel begins to corrode when exposed to air with normal humidity. Its recommended open-storage period is up to one year. After that, rust may form on the thread, making the nut difficult to screw onto a bolt.

Uncoated steel nuts are suitable for three main applications:

  • concealed connections inside valve bodies, pumps and equipment where moist air cannot enter;

  • dry, heated premises such as mechanical workshops, heating substations and server rooms;

  • assemblies intended for painting, as zinc coating can reduce paint adhesion, while paint adheres evenly to clean steel.

Uncoated steel nuts are not suitable for systems exposed to water or condensation, outdoor installation or roofing work. Zinc-plated nuts should be used in these conditions.

Food-processing facilities, swimming pools, marine environments and chemical plants require stainless steel nuts made of AISI 304 or AISI 316.

An uncoated steel nut should be paired with an uncoated steel bolt. Combining a zinc-plated bolt with a standard uncoated steel nut creates a connection with different levels of corrosion resistance, causing the nut to rust before the bolt.

Spanner Size and Nut Height

According to GOST 5915-70, the spanner sizes are:

  • M10 nut — 17 mm;

  • M12 nut — 19 mm;

  • M16 nut — 24 mm;

  • M20 nut — 30 mm.

The height of a standard nut is approximately 0.8 times the thread diameter. For example, an M10 nut is 8 mm high.

The property class is marked with the number 5 or 8 on the side of the nut and should match the property class of the bolt:

  • property class 5 nut for a class 5.8 bolt;

  • property class 8 nut for a class 8.8 bolt.

If a lower-class nut is installed on a high-strength bolt, the nut thread will strip before the bolt itself fails. General recommendations and guidelines for selecting bolt length for flanged connections are provided in the Nuts and Bolts sections.

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