
■ Recommended Bored Hole Size Table for American Dryseal Taper Pipe Threads (NPTF) (Refer to ANSI B1.20.3-1976, re-confirmed in 1982) unit: mm Bored Hole reference Minor Diameter Size (reference) Tap L3
Size L1 L1+L3+1P Pipe End Position of
| (3P) | Maximum | Basic | |||||||||
| (Basic Diameter Position) | ( L1+L3+1P ) | Size of | Diameter | ||||||||
| Maximum | Minimum | Maximum | Minimum | Straight | Position | ||||||
| Tolerance | Tolerance | Bored Hole | ℓg | ||||||||
| Value | Value | Value | Value |
| ① | ② | ③ | ④ | ⑤ | ⑥ | ⑦ | ⑧ | ⑨ | ⑩ | ⑪ | ⑫ | |
| NPTF | 1/16- 27 | 4.064 | 2.822 | 7.827 | 6.505 | 6.414 | 0.091 | 6.015 | 5.923 | 0.091 | 5.99 | 12.00 |
| NPTF | 1/8 - 27 | 4.102 | 2.822 | 7.865 | 8.852 | 8.761 | 0.091 | 8.362 | 8.270 | 0.091 | 8.34 | 12.05 |
| NPTF | 1/4 - 18 | 5.786 | 4.234 | 11.431 | 11.484 | 11.397 | 0.086 | 10.770 | 10.684 | 0.086 | 10.75 | 17.45 |
| NPTF | 3/8 - 18 | 6.096 | 4.234 | 11.741 | 14.923 | 14.836 | 0.086 | 14.189 | 14.103 | 0.086 | 14.17 | 17.65 |
| NPTF | 1/ 2- 14 | 8.128 | 5.443 | 15.386 | 18.419 | 18.333 | 0.086 | 17.459 | 17.373 | 0.086 | 17.44 | 22.85 |
| NPTF | 3/4 - 14 | 8.611 | 5.443 | 15.868 | 23.764 | 23.678 | 0.086 | 22.773 | 22.687 | 0.086 | 22.75 | 22.95 |
| NPTF | 1 - 11.5 | 10.160 | 6.627 | 18.996 | 29.812 | 29.726 | 0.086 | 28.625 | 28.538 | 0.086 | 28.60 | 27.40 |
| NPTF | 11/4 - 11.5 | 10.668 | 6.627 | 19.504 | 38.569 | 38.483 | 0.086 | 37.350 | 37.263 | 0.086 | 37.33 | 28.10 |
| NPTF | 11/ 2- 11.5 | 10.668 | 6.627 | 19.504 | 44.639 | 44.552 | 0.086 | 43.420 | 43.334 | 0.086 | 43.40 | 28.40 |
| NPTF | 2 - 11.5 | 11.074 | 6.627 | 19.910 | 56.677 | 56.590 | 0.086 | 55.432 | 55.345 | 0.086 | 55.41 | 28.00 |
HAND ENGAGEMENT(L1)+L3 + ONE TURN FULL THREAD Remarks 1. Pipe End is Basic Diameter Position (E1).
L 3 3p L1 Remarks 2. Effective Thread Length is the length away from Pipe End
by (L1+L3+1P). NPTF INTERNAL THREAD Remarks 3. Concerning bored hole shape, considering load on taps, taper bored hole is recommended. NPTF EXTERNAL THREAD Remarks 4. When applying taper bored hole, by referring to values
before reaming by taking reamer's margin into account.
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.