Coupling Nuts

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Coupling Nuts Basics

Coupling nuts are elongated internally threaded nuts used for joining two male-threaded fasteners, usually threaded all thread rods, in a variety of applications where extending the length or attaching like items is required. The outside of a coupling nut is usually hex shaped so that a wrench can tighten or loosen it.

Coupling nuts are available in different grades and finishes based on the mechanical and chemical properties of the material, and the intended application of the coupling nut.

Coupling Nuts Grades & Markings

Coupling nuts are available in different grades based on the mechanical and chemical properties of the material, and the intended application of the coupling nut.

Grade 2 Coupling Nuts

These coupling nuts will either conform to SAE J995 Grade 2 or ASTM A563 Grade A, both of which are manufactured from carbon steel and are equivalent in strength. Grade A & Grade 2 require no material marking.

18-8 Stainless Steel Coupling Nuts

18-8 stainless steel hex coupling nuts are made from one of the following austenitic alloys: 303, 303Se, 304, XM7, all of which are characterized as having a chromium content of 17-19% and nickel content of 8-10%. 18-8 Stainless Steel requires no material marking.

Common Finishes of Coupling Nuts

Coupling nuts are available in a variety of finishes and coatings, which play a role in the suitability of the fasteners in different applications, such as enhancing resistance to corrosion from environmental elements or chemicals. Coatings also greatly effect consistency of torque values for installation, and ease of disassembly at the end of service.

Galvanized Coupling Nuts

Coupling nuts are coated with a sacrificial zinc coating that acts as an anode to prevent the fastener underneath from corroding.

  • Hot Dipped Galvanized: Fasteners are dipped in a bath of molten zinc.

Plated Coupling Nuts

Coupling nuts are coated with a thin layer of zinc, typically via electroplating.

  • Coupling nuts will not corrode as quickly when covered with this protective coating, even when a scratch or cut exposes the steel to air or moisture. Zinc or cadmium plating acts as a sacrificial anode, and will always tarnish and corrode first thereby protecting the steel underneath.