- This page provided the thread dimensions of 1/4 - 18 NPTF
- NPTF stands for National Pipe Thread Fuel, based on ASTM B1.20.3.
- It is also called Dryseal Pipe Thread.
- It is a variation of the more popular NPT thread standard based on ASTM B1.20.1.
- Learn more about NPTF and the difference between NPTF and NPT
1/4 - 18 NPTF - External Basic Thread Dimensions
For interpertations of the terms scroll down to the drawings below the table
| Property | Inch | mm |
|---|---|---|
| Nominal Pipe Size(∅) | 1/4 | |
| Pipe Outside Diameter (D) | 0.54 | 13.72 |
| Fitting Outside Diameter (D2) | 0.546 | 13.87 |
| Pitch - TPI (P) | 18 | ... |
| Pitch - Distance (P) | 0.055556 | 1.4111 |
| Thread Tapper Angle (β) | 1.7893 ° | |
| Thread V half Angle (α) | 30 ° | |
| Height of sharp V (H) | 0.048110 | 1.222 |
| Thread Height (h) | 0.03946 | 1.002 |
| Root Truncation (fr) | 0.0052 | 0.132 |
| Crest Truncation (fc) | 0.00345 | 0.088 |
| End of Thread Pitch Diameter (E0) | 0.47739 | 12.126 |
| Hand-Tight Engagement Length (L1) | 0.22780 | 5.786 |
| Pitch Diameter at L1 plane (E1) | 0.49163 | 12.487 |
| Length of Last usefull Thread (L2) | 0.40180 | 10.206 |
| Pitch Diameter at L2 plane (E2) | 0.50250 | 12.764 |
| Overall Thread Length (L2 + 3P) | 0.56250 | 14.288 |
| Length of Vanish threads (V) | 0.16070 | 4.082 |
1/4 - 18 NPTF - External Thread Drawing
Overview Drawing
Profile Drawing
1/4 - 18 NPTF - Internal Basic Thread Dimensions
For interpertations of the terms scroll down to the drawings below the table
| Property | Inch | mm |
|---|---|---|
| Nominal Pipe Size(∅) | 1/4 | |
| Pitch - TPI (P) | 18 | ... |
| Pitch - Distance (P) | 0.055556 | 1.4111 |
| Thread Tapper Angle (β) | 1.7893 ° | |
| Thread V half Angle (α) | 30 ° | |
| Height of sharp V (H) | 0.5460 | 1.411 |
| Thread Height (h) | 0.03946 | 1.002 |
| Root Truncation (fr) | 0.0052 | 0.132 |
| Crest Truncation (fc) | 0.00345 | 0.088 |
| Pitch Diameter at the end of the thread (E1) | 0.49163 | 12.487 |
| Hand-Tight Engagement Length (L1) | 0.22780 | 5.786 |
| Length of Wrenching Allowance (L3) | 0.16670 | 4.234 |
| Pitch Diameter at L3 plane (E3) | 0.46700 | 11.862 |
| Ideal Tap Drill Size | 0.43150 | 10.96 |
| Nearest standard Inch drill | 7/1 6 (0.438) |
1/4 - 18 NPTF - Internal Thread Drawing
Overview Drawing
Profile Drawing
1/4 - 18 NPTF - Tolerances
| Property | Minimum | Maximum |
|---|---|---|
| Thread Height (h) | 0.037710" (0.958 mm) | 0.041210" (1.047 mm) |
| Root Truncation (fr) | 0.00430" (0.109 mm) | 0.00610" (0.155 mm) |
| Crest Truncation (fc) | 0.00260" (0.066 mm) | 0.00430" (0.109 mm) |
| Tapper Angle (β) | 1.643° | 1.934° |
| Thread Head half Angle (α) | 28° | 32° |
* All other dimensions can be controlled only with gauges.
