Coupling Nuts

Coupling nuts are internally threaded fasteners that join threaded rods, pipes, and other threaded parts, sometimes parts of differing sizes.

Finish

Plain

Nothing has been done to this bare metal surface to improve appearance or corrosion resistance, which is very low if the material is steel. Often the surface has been oiled which improves lubricity. This finish is susceptible to rusting and corrosion in exterior environments. This most basic finish can be used when protection is not an issue or indoors.
Zinc

This finish, also know as zinc plating, zinc chromate or dichromate provides good corrosion resistance and is the standard for many hardware fasteners. It is an electroplated zinc layer covered with a chromate post-treatment. The zinc protects the steel from corrosion and the chromate layer protects the zinc from degrading. It is a popular finish because of its protection, value, and ease of coating. Slightly less corrosion resistant than yellow zinc, it is a versatile finish that is best used indoors. This finish should not be used in marine or high salt spray environments.

Grade

18-8

A general designation for the most common and popular stainless steel, (300 Series) referring to the 18% chromium and 8% nickel. It's strength has a range from the middle to low end of the grade scale. All 300 series stainless steel share the ratio of chromium to nickel with varying other elements improving different properties. It has higher corrosion resistance than the 400 series stainless steels and it is non-magnetic.
316

The second most common stainless steel grade, this material is stronger than grade 2, slightly weaker than grade 5,or generally as strong as medium to low carbon steel. It is on the low middle end of the grade scale. It is used in more severe corrosive environments than 304 stainless steel, as such it is used in more industrial settings, like process chemicals, textiles, bleaches, salt water and rubber. It is also used in surgical implants. The DIN/ISO denotation for a very similar grade is A4-70.

Material

Stainless Steel

Stainless steel is steel combined with alloying elements, principally chromium, to enhance corrosion resistance and impart other desired properties depending upon the alloying elements in use and their proportions. Many stainless steel fasteners are non-magnetic or less magnetic than regular steel fasteners.
Steel

Steel is the most common fastener material due to its strength properties. Unalloyed steel may be surface treated to enhance corrosion resistance and other desirable properties.

Specification

DIN 6334

German Standards for hexagon coupling nuts.

Type

Coupling Nut

Coupling nuts are internally threaded fasteners that join threaded rods, pipes, and other threaded parts.
Coupling Nut - Reducing

Reducing coupling nuts join studs or threaded rods of different diameters.