How it connects
Straight mechanical screw thread that fastens the aerator assembly onto the spout, creating a fluid seal against an internal flat rubber or elastomer gasket rather than on the thread flanks.
Male and female halves
Female internal straight thread (2B class fit) designed to mate with an external male 55/64-27 UNS straight thread found on faucet spout ends or dual-thread aerators.
Usually connects to
- Matching male 55/64-27 UNS faucet outlet or adapter
- Corresponding dual-thread aerator adapter, described as 15/16-27 male / 55/64-27 female
Common sizes
- One 55/64-27 size: nominal diameter 0.859 in (21.8–21.828 mm), 27 TPI, about 0.941 mm pitch. Nominal major diameter is not the female opening measurement.
Where it is used
residential plumbingcommercial plumbingfaucet spouts and aeratorsKitchen and bathroom faucet aeratorsFaucet attachment adapters
Variations
- Standard dual-thread aerator housings (combining 15/16-27 male outer thread and 55/64-27 female inner thread)
How to recognise it
Internal straight fine thread located inside an aerator housing or spout fitting with an inner diameter of approximately 0.82 to 0.86 inches, usually seating against an internal flat sealing washer.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| 15/16-27 UNS male aerator thread | 15/16-27 is male (external) and slightly larger (~0.938 in), often integrated into the outside of dual-threaded aerators while 55/64-27 is female (internal). A larger external thread, often offered alongside the 55/64-27 female thread on dual-thread faucet adapters. Same pitch does not make the diameters interchangeable. |
| M22x1 metric aerator thread | M22x1 has a 22 mm diameter and 1.0 mm metric pitch (~25.4 TPI); threads will bind after 1-2 turns when cross-threaded with 55/64-27 UNS (27 TPI). |
Also called
55/64"-27 UNS-2B55/64-27 female aerator threadSmall faucet aerator thread55/64 in.-27F
Good to know
55/64-27 UNS female is the most ubiquitous standard aerator thread size in North American residential faucets alongside 15/16-27 male. Many commercial aerators feature dual threading incorporating both.
Related connections
Design with real parts
Crafti checks which parts connect, right in your browser.