Coupling, Bushing, Nipple or Adapter? Pipe Fitting Names Explained
6 min read · updated Oct 2026
Male and female: the one idea you need
Every threaded end is either male (threads on the outside, like a bolt) or female (threads on the inside, like a nut). Store shelves and catalogs use short codes for this: MIP or MNPT means male pipe thread, and FIP or FNPT means female pipe thread. Once you know the gender of both ends and their sizes, you know what to ask for.
| Name | Ends | Sizes | Used for |
|---|---|---|---|
| Coupling | Female × Female | Same or different | Joining two pipes end to end |
| Reducer bushing | Male × Female | Male bigger than female | Stepping a large port down to a smaller pipe |
| Nipple | Male × Male | Same or different | Joining two female fittings or valves |
| Street fitting | Male × Female | Same size | Extending a port without an extra nipple |
| Adapter | Any | Any | Crossing between thread systems (NPT, BSP, hose) |
Coupling (female × female)
A coupling is a short sleeve with inside threads at both ends. You screw a pipe into each side to join them in a straight line. When both sides are the same size it's just a "coupling". When they differ, it's a reducing coupling (sometimes called a bell reducer, after its shape). The example below joins a 3/4" pipe to a 1" pipe.
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Reducer bushing (male × female, nested)
A bushing screws into a large female port and gives you a smaller female port in the middle. Because the small socket sits inside the big outer thread, a bushing is much shorter than a coupling. That makes it the go-to part when space is tight, for example on a pump, tank or water heater outlet. The example is a 1" male bushing with a 3/4" female socket inside it.
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Nipple (male × male)
A nipple is a short piece of pipe with outside threads on both ends. You use one to connect two female parts, such as a valve and a tee. A hex nipple has a six-sided band in the middle so you can grip it with a wrench. A close nipple is so short that the threads almost meet in the middle. If the two ends are different sizes, it's a reducing nipple, like this 3/4" to 1" example.
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Street fitting (male × female, same size)
"Street" means one end is male and the other is female, at the same size. You can screw it straight into an existing fitting without adding a nipple first. You'll mostly hear the word on elbows ("street elbow"), but a straight version works as a short extension that moves a connection out past a wall or a crowded spot.
Drag the 3D model to spin · scroll to zoom
Adapter: when the thread systems differ
Plumbers use "adapter" for any part that crosses between two different systems: American NPT to British BSP, garden hose (GHT) to pipe, threaded pipe to a hose barb, or copper to plastic. The shape can be any of the ones above. What makes it an adapter is that the two ends follow different standards.
How to order the right part
Name the larger size first, then the smaller, then each end's gender and thread type. For example: 1" MNPT × 3/4" FNPT hex bushing. If you're not sure of a size, measure the outside of a male thread or the inside of a female thread and compare it with a size chart. Pipe sizes are nominal, so a "1 inch" thread is actually about 33 mm across.
Design your own adapter
Choose a thread for each end, set the lengths, and download a ready-to-print model with a full water passage.
Open the designer →More reading: all thread guides.