Cap Nuts

Cap nuts are fasteners with a dome-shaped cap. Their manufacture is governed by GOST 11860 (foreign equivalent — DIN 1587).

Key provisions of GOST 11860

The GOST standard sets several parameters at once:

• Thread. Parts are made with both fine and coarse thread. Only M8, M10, M14, M24 nuts are produced with fine thread.
• Width across flats. GOST covers parts for wrench sizes from 5.5 mm to 36 mm.
• Weight. Depending on size, 1000 pieces weigh from 920 g to 192.6 kg.
• Minimum height across flats. Under GOST this parameter is 2.75–15 mm.

All parameters must be considered together when selecting a cap nut — this ensures a reliable connection of the parts.

DIN 1587 standard

Fasteners from foreign manufacturers comply with DIN 1587. The standard sets permissible dimensions of the hardware and the materials of manufacture. Cap nuts can be made from the following materials:

• Carbon steel, alloy steel.
• Stainless steel.
• Structural steel.
• Non-ferrous metal.
• Plastic.

Steel fasteners may have an electroplated coating. Under DIN 1587 fasteners correspond to the following dimensions:

• Width across flats — 6.5–34 mm.
• Height of flats — 3.2–19 mm.
• Overall height of the part — 8–42 mm.
• Cap diameter — 6.5–34 mm.

The shape of the cap base is not regulated by the standard.

Advantages and disadvantages of cap nuts

Fasteners of this type are widely used due to a number of advantages:

1. Low injury risk. The cap covers the protruding parts of the threaded connection, and its shape prevents injury.
2. Corrosion protection. The design of the fastener prevents moisture and dirt from reaching the threaded connection, which protects the metal parts from corrosion. The lubricant on the threaded connection is preserved throughout the service life of the part.
3. Appearance. The spherical cap hides the threaded connection, giving the product an aesthetic look.

The disadvantages include a restriction on use with long bolts or studs: the inner part of the sphere rests against the bolt, and the nut cannot be fully tightened. This should be taken into account when selecting a cap nut.

Thanks to their design features, fasteners of this type are used in mechanical engineering, instrument and equipment manufacturing, the food industry and other sectors. Correct selection of a cap nut ensures a strong and reliable connection, protected from external effects.