Nuts Used to Join Two Male Threads
Coupling nuts are threaded fasteners used to join two male threads, most commonly threaded rod. The outside of a coupling nut is typically a hex to be driven with a wrench. Coupling nuts are also used to make up long rod assemblies from shorter lengths of rods.
Coupling nuts can only connect two male threads of the same thread diameter. They can be used to tighten a rod assembly inward or to press a rod assembly outward. The industrial fastener institute describes coupling nut dimensions in standard IFI-128. Coupling nuts come in stainless steel (304 & 316), aluminum, hot-dipped galvanized steel, and zinc-plated steel finishes.
18-8 or 304 grades of Stainless steel are suitable for many general purpose applications, especially freshwater and non-salt water wet environments. Corrosion-resistant and durable, 18-8 stainless steel is equivalent to the A2 grade of stainless steel.
For much more corrosive environments, such as in saltwater or marine applications, 316 stainless steel is the ideal choice. 316 Stainless steel is equivalent to A4 stainless steel.
Zinc Plated Steel
Zinc is by far the most common and economical type of plating for fasteners. The zinc plating adds a protective "sacrificial" top layer against corrosion while also adding a shiny finish to the fastener. Zinc plating is ideal for indoor use, where it won't be constantly exposed to harsh elements.
Zinc plated coupling nuts come in either US sized A563 Grade A steel or Metric sized DIN6334 Class 6 steel.
Hot Dip Galvanized Steel
Hot-dip galvanizing is done by submerging the fastener in molten zinc to provide a corrosion protecting finish. Essentially, the added zinc that's applied through the galvanization process serves as a "sacrificial" layer of protection to keep the steel underneath from degrading or being damaged.
You'll find hot-dip galvanized fasteners frequently used in situations where corrosion resistance is needed without the cost of stainless steel. It is considered superior to stainless steel in terms of cost and life-cycle. For applications where the fastener will constantly be exposed to corrosive materials, you'll want to use stainless steel instead.
Note: hot-dip galvanized fasteners tend to be a little larger, with thicker threading, because of the added layer of zinc. To compensate, hot-dip galvanized nuts are tapped larger to be thread effectively on hot-dip galvanized bolts. You will have difficulty trying to fasten non-hot-dip galvanized nuts to hot-dip galvanized bolts, screws, or all thread.
Aluminum is a strong, durable, easily formed, and lightweight metal that is excellent for use in fasteners where strength-to-weight properties are a major requirement. Aluminum has the best strength-to-weight ratio of any metal in common use and corrosion resistance on par with stainless steel.
What is an extension nut?
An extension nut is a kind of fastener nut used to join two male threads together, such as multiple threaded rod pieces. Extension nut is a much broader name for coupling nuts, which connect two male threads of the same thread size, and reducer nuts, which connect two male threads of different sizes.
What are coupling nuts used for?
Coupling nuts are used to connect two male threads, usually threaded rods or pipes. Typically hexagonal in shape to be grabbed by a wrench, they tighten rod assemblies or extend them further outward.
What are reducer nuts used for?
Reducer nuts, or reducer coupling nuts, are used to connect two different sized male threads, usually threaded rods or pipes. Typically hexagonal in shape to be grabbed by a wrench, they tighten rod assemblies or extend them further outward, even if they have different thread sizes.
How do you join two threaded rods together?
Join threaded rods together by using coupling nuts. You can join any two externally threaded rods or bolts with coupling nuts, so long as they are of the same body diameter and pitch. If the body diameter and pitch are different between the two, use reducer coupling nuts to connect them.
What are long nuts called?
Long nuts are another name for extension nuts, otherwise known as coupling nuts or coupling reducer nuts.