
Unit:mm
| Size | L1 | L3 (3P) | L1+L3+1P | (Basic | Pipe End Diameter Po | Minor Di sition) | ameter ( | Position of L1+L3+1P | ) | Bored Hole Size (reference) Maximum Size of | reference Tap Basic Diameter | |
| Maximum Value | Minimum Value | Tolerance | Maximum Value | Minimum Value | Tolerance | Straight Bored Hole | Position ℓg | |||||
| ① | ② | ③ | ④ | ⑤ | ⑥ | ⑦ | ⑧ | ⑨ | ⑩ | ⑪ | ⑫ | |
| 1/16- 27 | NPTF | 4.064 | 2.822 | 7.827 | 6.505 | 6.414 | 0.091 | 6.015 | 5.923 | 0.091 | 5.99 | 12.00 |
| 1/8- 27 | NPTF | 4.102 | 2.822 | 7.865 | 8.852 | 8.761 | 0.091 | 8.362 | 8.270 | 0.091 | 8.34 | 12.05 |
| 1/4- 18 | NPTF | 5.786 | 4.234 | 11.431 | 11.484 | 11.397 | 0.086 | 10.770 | 10.684 | 0.086 | 10.75 | 17.45 |
| 3/8- 18 | NPTF | 6.096 | 4.234 | 11.741 | 14.923 | 14.836 | 0.086 | 14.189 | 14.103 | 0.086 | 14.17 | 17.65 |
| 1/2- 14 | NPTF | 8.128 | 5.443 | 15.386 | 18.419 | 18.333 | 0.086 | 17.459 | 17.373 | 0.086 | 17.44 | 22.85 |
| 3/4- 14 | NPTF | 8.611 | 5.443 | 15.868 | 23.764 | 23.678 | 0.086 | 22.773 | 22.687 | 0.086 | 22.75 | 22.95 |
| 1 - 111/2 | NPTF | 10.160 | 6.627 | 18.996 | 29.812 | 29.726 | 0.086 | 28.625 | 28.538 | 0.086 | 28.60 | 27.40 |
| 11/4- 111/2 | NPTF | 10.668 | 6.627 | 19.504 | 38.569 | 38.483 | 0.086 | 37.350 | 37.263 | 0.086 | 37.33 | 28.10 |
| 11/2- 111/2 | NPTF | 10.668 | 6.627 | 19.504 | 44.639 | 44.552 | 0.086 | 43.420 | 43.334 | 0.086 | 43.40 | 28.40 |
| 2 - 111/2 | NPTF | 11.074 | 6.627 | 19.910 | 56.677 | 56.590 | 0.086 | 55.432 | 55.345 | 0.086 | 55.41 | 28.00 |
Remarks 1. Pipe End is Basic Diameter Position (E1).
| HAND ENGAGEMENT(L1)+L3 | Remarks 2. | Effective Thread Length is the length |
| + ONE TURN FULL THREAD | away from Pipe End by (L1+L3+1P). | |
| Remarks 3. | Concerning bored hole shape, considering load | |
| L L 3= 3p | ||
| on taps, taper bored hole is recommended. | ||
| Remarks 4. | When applying taper bored hole, by referring | |
| NPTF INTERNAL THREAD | to values shown in columns ⑤ , ⑥ and ⑧ , | |
| ⑨ , prepare the taper hole by using pipe | ||
| NPTF EXTERNAL THREAD | reamer (1/16 taper). By referring to values | |
| in shown column ⑪ , select the drill | ||
| diameter before reaming by taking reamer's | ||
| margin into account. | ||
| Remarks 5. | When preparing straight bored hole, by |
referring to values shown in column ⑪ , select drill diameter.
internal Basic Major Dia. − Hole Size Before Tapping threads
As shown above, when the thread height increases, the amount of material to be removed increases rapidly, so it is an advantage to tap users to keep the hole size (thread minor diameter) as large as possible.