Coupling nuts are a type of fastener used to connect two threaded rods or studs. They are typically hexagonal in shape and have internal threads that match the external threads of the rods they are connecting. These nuts are designed to join two pieces of threaded material together securely.

Key features of coupling nuts include:

1. Hexagonal Shape: Most coupling nuts have a hexagonal shape, allowing them to be easily tightened or loosened using a wrench or other tools.
2. Internal Threads: The inside of the coupling nut is threaded, allowing it to screw onto the external threads of a threaded rod or stud.
3. Various Materials: Coupling nuts can be made from different materials such as steel, stainless steel, brass, or other alloys, depending on the application and the required strength or corrosion resistance.
4. Available Sizes: They come in various sizes to accommodate different diameters and thread pitches of the rods they are connecting.
5. Length: The length of the coupling nut can vary, providing flexibility in how much distance it adds between the two connected rods.

Coupling nuts are commonly used in construction, plumbing, and other applications where it is necessary to extend the length of threaded rods or to connect two threaded components. They are also used in situations where periodic disassembly and reassembly are required.

It’s important to choose coupling nuts that match the specifications of the threaded rods or studs you are working with to ensure a secure and proper connection.