Faucet Aerator Thread Standards
Direct Answer
Faucet aerators utilize standardized ultra-fine metric and imperial screw threads to attach flow restrictors and stream straighteners to residential and commercial spouts. Common sizes include Standard M24×1.0 male, 55/64"-27 female, Junior M18.5×1.0, and Tom Thumb M16.5×1.0, engineered for EPA WaterSense flow compliance.
Source: ASME A112.18.1 / CSA B125.1
Specs
| Standard Governing Body | ASME A112.18.1 / CSA B125.1 / NSF 61 |
| Standard / Regular Size (Metric) | M24 × 1.0 mm (Male) | M22 × 1.0 mm (Female) |
| Standard / Regular Size (US Imperial) | 15/16"-27 UNS (Male) | 55/64"-27 UNS (Female) |
| Junior Size | M18.5 × 1.0 mm (Male) | 13/16"-27 UNS (Female) |
| Tom Thumb / Tiny Junior | M16.5 × 1.0 mm (Male) | 5/8"-27 UNS (Female) |
| Standard WaterSense Flow Rate | 1.2–1.5 GPM (bathroom) | 1.8–2.2 GPM (kitchen) |
| Sealing Method | EPDM rubber flat washer compressed against spout shoulder |
Standard, Junior, and Tom Thumb Sizing Categories
Modern kitchen and bathroom spouts utilize three primary aerator dimensional categories:
- Standard / Regular (Quarter Size): The most common global size (~$24\text{ mm}$ outer diameter). Male spouts use $M24 \times 1.0\text{ mm}$ metric threads (or US $15/16\text{"-27 UNS}$); female spouts use $55/64\text{"-27 UNS}$ or $M22 \times 1.0\text{ mm}$.
- Junior (Nickel Size): Medium compact spouts (~$18.5\text{ mm}$ outer diameter), utilizing $M18.5 \times 1.0\text{ mm}$ male or $13/16\text{"-27 UNS}$ female threads.
- Tom Thumb / Tiny Junior (Dime Size): Slim designer faucets (~$16.5\text{ mm}$ outer diameter) utilizing $M16.5 \times 1.0\text{ mm}$ male or $5/8\text{"-27 UNS}$ female threads.
Hidden Cache Aerators and Flow Regulation
Modern minimalist designer spouts frequently feature Cache (hidden) aerators that thread directly inside the faucet spout without an exposed chrome metal collar. These require a dedicated plastic multi-toothed removal key (color-coded by diameter: regular red/green, junior yellow, tiny junior blue) for replacement and sediment cleaning. Standard EPA WaterSense compliance limits maximum flow to $1.5\text{ GPM}$ ($5.7\text{ L/min}$) for residential lavatory taps.