Short definition
A nipple is a short length of pipe (under 12 inches) with male threads on both ends. It’s used to extend a fitting, span a small gap, or connect two female-threaded fittings. Standard sizes by length: close nipple (no unthreaded shoulder, threads run end-to-end), short (minimal shoulder), and long (substantial unthreaded mid-section).
What it is
Nipples come in galvanized steel, black iron, and brass — matched to the system they’re being installed in. Brass nipples are common at water-heater connections (sometimes paired with dielectric isolation), and hex nipples include a hexagonal mid-section that gives a wrench somewhere to grip.
Why it matters to a homeowner
You’ll buy nipples for plumbing repairs in threaded systems — water-heater nipple replacement, adding a fixture in a basement laundry, extending a fitting that’s recessed into a wall. The most common homeowner replacement is a corroded steel nipple at a water-heater port; a brass nipple is the standard upgrade.
Common variants and what a nipple is not
- Close, short, long. Distinguished by length and the amount of unthreaded shoulder.
- Brass vs. steel nipple. Brass for corrosion resistance and water-heater connections; steel (galvanized or black iron) for general gas or water service.
- Hex nipple. Standard nipple with a hexagonal middle for wrench grip.