Garden Hose Thread (GHT / ANSI B1.20.7)
Direct Answer
Garden Hose Thread (GHT) is the standardized North American outdoor water coupling governed by ANSI/ASME B1.20.7. Specified as 3/4"-11.5 NH, it features a straight, non-tapered thread with a 1.0625-inch (27.0 mm) major diameter that seals via axial compression against a flat rubber washer inside the female swivel coupling.
Source: ANSI/ASME B1.20.7-1991 (R2018)
Specs
| Standard Governing Body | ANSI / ASME B1.20.7 |
| Thread Designation | 3/4"-11.5 NH (National Hose) |
| Major Diameter (Male Outer ø) | 1.0625 inches (27.0 mm) |
| Thread Pitch | 11.5 TPI (2.209 mm pitch) |
| Thread Form & Flank Angle | 60° American National straight parallel thread |
| Sealing Mechanism | Flat elastomeric washer compressed in female swivel seat |
| Operating Water Pressure | 40–80 PSI typical residential (up to 150 PSI burst) |
Parallel Thread Mechanics and Washer Compression
Unlike tapered pipe threads (such as NPT), GHT is a straight parallel thread ($0^\circ$ taper). The threads perform solely as a mechanical clamp to pull the male nose flat against a rubber or silicone O-ring/washer seated inside the female swivel coupling. Hand-tightening or gentle quarter-turn wrench torque provides complete water sealing up to standard municipal pressures ($60\text{–}80\text{ PSI}$).
GHT vs 3/4-inch NPT Distinction
A common plumbing error is attempting to screw a $3/4\text{-inch NPT}$ pipe fitting directly into a $3/4\text{-inch GHT}$ garden hose outlet. While both share the same nominal $3/4\text{-inch}$ designation and $11.5\text{ TPI}$ pitch:
- GHT has a fixed outer diameter of $1.0625\text{ in}$ ($27.0\text{ mm}$) and parallel walls.
- NPT has a tapered outer diameter ($1.050\text{ in}$ at small end to $1.060\text{ in}$ at gauge plane).
An NPT fitting will thread approximately 1 to 2 turns before binding without compressing the internal washer, resulting in high-pressure spraying. Dedicated $3/4\text{" GHT to } 3/4\text{" NPT}$ brass adapters are required to transition between garden hoses and rigid pipework.