aerators on kitchen faucets

an aerator

An aerator, showing an external, male thread, which would screw into a female threaded faucet.

In most modern U.S. kitchen faucets, both the inside and outside of the faucet tip are threaded, to make it possible to screw on aerators, hose adapters, and so forth. The inside thread of the faucet is usually 55/64 inch × 27 threads per inch, and the exterior (male) thread is 15/16 inch × 27 tpi.

A smaller size is regularly used by some faucet makers (e.g., Kohler and Price Pfister). The extrenal, male thread is 13/16 × 27 tpi. The internal, female thread is ¾ × 27 tpi.

Plumbers have a quick test for aerator sizes. A U.S. quarter coin will just cover 15/16 male external threads, while a nickel will fit inside 15/16 female threads. A nickel will cover 13/16 male external threads, while a dime will fit inside 13/16 inside threads.

Notice that the male threads called 15/16 or 13/16 are really that size, while the female 15/16 is actually 55/64″ and the female 13/16 is actually 3/4″.

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