How it connects
Straight parallel machine threads screw together to compress an internal elastomeric flat washer or O-ring against the spout seat to form a watertight seal; threads do not seal.
Male and female halves
Male external thread on a faucet spout, adapter, or aerator insert; mates into a matching female internal threaded collar or spout body.
Usually connects to
- Matching female-thread aerator housing, spout, adapter or coupler; match the specified thread, including 15/16-27 examples
- A 55/64-27 female spout is another listed size and requires its corresponding male thread
Common sizes
- Regular size 15/16-27 UNS: nominal 23.8125 mm diameter and 0.94074 mm pitch; exact fit tolerance and engagement are not established.
- Other aerator sizes include 55/64-27, junior 13/16-27, 3/4-27 and Tom Thumb M16 × 1.0.
- Metric counterparts are described as M24 × 1.0 for regular and M18.5 for junior; confirm the actual metric or inch thread rather than assuming interchangeability.
Where it is used
residential plumbingcommercial plumbingfaucet aerators and adaptersKitchen and bathroom faucet aeratorsFaucet outlet adapterslavatory bathroom faucets
Variations
- Regular 15/16-27, 55/64-27, junior 13/16-27 or 3/4-27 UNS-2A male
- External-only housing
- Dual housing with external 15/16-27 and internal 55/64-27
- Metric M24 × 1.0 or M18.5 × 1.0
How to recognise it
External parallel threads on a faucet spout outlet or aerator adapter with a very fine 27 TPI pitch and typical nominal outside diameter around 55/64" (~21.8 mm) or 15/16" (~23.8 mm), sealing against an internal washer recess.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| Metric Faucet Aerator Thread (M24x1, M22x1, M18x1) | Metric aerator threads use a 1.0 mm pitch (~25.4 TPI) and metric diameters, whereas UNS aerator threads standardly feature 27 threads per inch (0.941 mm pitch). |
| NPT / NPSM Thread | NPT has tapered threads with coarser pitch (e.g. 1/2"-14 or 3/8"-18); UNS aerator threads are parallel, fine 27 TPI, and seal via flat rubber washers. |
| GHT (Garden Hose Thread) | GHT is 3/4"-11.5 NH with coarse rounded threads and much larger pitch, requiring an aerator-to-hose adapter. |
| Female faucet aerator thread (55/64"-27 UNS) | That aerator has internal threads for an externally threaded faucet. This interface has external 15/16-27 threads. Female aerator thread is internal (threads inside the aerator collar to screw onto external spout threads), whereas male aerator thread is external. |
| NPT pipe thread | This is a straight faucet-end thread with washer sealing; verify the 15/16-inch diameter and 27-TPI pitch rather than treating it as a nominal pipe size. |
Also called
Faucet Aerator Spout Male Thread55/64"-27 Male Thread13/16"-27 Male Thread15/16-27 male aerator thread; 15/16"-27 UNS male thread15/16-27MM24x1 male aerator threadMale tap aerator thread
Good to know
While 27 TPI is the nearly universal thread pitch for North American imperial aerators, nominal diameters vary across standard regular (15/16" male, 55/64" female/male) and small/junior sizes (13/16", 3/4").
Related connections
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