- This page provided the thread dimensions of 2 1/2 - 8 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
2 1/2 - 8 NPTF - External Basic Thread Dimensions
For interpertations of the terms scroll down to the drawings below the table
| Property | Inch | mm |
|---|---|---|
| Nominal Pipe Size(∅) | 2 1/2 | |
| Pipe Outside Diameter (D) | 2.875 | 73.03 |
| Fitting Outside Diameter (D2) | 2.893 | 73.48 |
| Pitch - TPI (P) | 8 | ... |
| Pitch - Distance (P) | 0.125 | 3.175 |
| Thread Tapper Angle (β) | 1.7893 ° | |
| Thread V half Angle (α) | 30 ° | |
| Height of sharp V (H) | 0.108250 | 2.75 |
| Thread Height (h) | 0.094 | 2.388 |
| Root Truncation (fr) | 0.0082 | 0.208 |
| Crest Truncation (fc) | 0.00605 | 0.154 |
| End of Thread Pitch Diameter (E0) | 2.71953 | 69.076 |
| Hand-Tight Engagement Length (L1) | 0.68200 | 17.323 |
| Pitch Diameter at L1 plane (E1) | 2.76216 | 70.159 |
| Length of Last usefull Thread (L2) | 1.13750 | 28.893 |
| Pitch Diameter at L2 plane (E2) | 2.79062 | 70.882 |
| Overall Thread Length (L2 + 3P) | 1.51560 | 38.496 |
| Length of Vanish threads (V) | 0.37810 | 9.604 |
2 1/2 - 8 NPTF - External Thread Drawing
Overview Drawing
Profile Drawing
2 1/2 - 8 NPTF - Internal Basic Thread Dimensions
For interpertations of the terms scroll down to the drawings below the table
| Property | Inch | mm |
|---|---|---|
| Nominal Pipe Size(∅) | 2 1/2 | |
| Pitch - TPI (P) | 8 | ... |
| Pitch - Distance (P) | 0.125 | 3.175 |
| Thread Tapper Angle (β) | 1.7893 ° | |
| Thread V half Angle (α) | 30 ° | |
| Height of sharp V (H) | 2.8930 | 3.175 |
| Thread Height (h) | 0.094 | 2.388 |
| Root Truncation (fr) | 0.0082 | 0.208 |
| Crest Truncation (fc) | 0.00605 | 0.154 |
| Pitch Diameter at the end of the thread (E1) | 2.76216 | 70.159 |
| Hand-Tight Engagement Length (L1) | 0.68200 | 17.323 |
| Length of Wrenching Allowance (L3) | 0.37500 | 9.525 |
| Pitch Diameter at L3 plane (E3) | 2.69610 | 68.481 |
| Ideal Tap Drill Size | 2.60540 | 66.177 |
| Nearest standard Inch drill | 2 39/64 (2.609) |
2 1/2 - 8 NPTF - Internal Thread Drawing
Overview Drawing
Profile Drawing
2 1/2 - 8 NPTF - Tolerances
| Property | Minimum | Maximum |
|---|---|---|
| Thread Height (h) | 0.091850" (2.333 mm) | 0.096150" (2.442 mm) |
| Root Truncation (fr) | 0.00690" (0.175 mm) | 0.00950" (0.241 mm) |
| Crest Truncation (fc) | 0.00520" (0.132 mm) | 0.00690" (0.175 mm) |
| Tapper Angle (β) | 1.643° | 1.934° |
| Thread Head half Angle (α) | 28.5° | 31.5° |
* All other dimensions can be controlled only with gauges.
