E3 E0 E1 D Description of productsTechnical Information 15. Bored hole size before tapping ( for thread cutting ) ■ Recommended Bored Hole Size Table for American Taper Pipe Threads (NPT) (Refer to ANSI/ASME B1.20.1-1983) Unit:mm Bored Hole reference Minor Diameter Size (reference) Tap Size L1 L3 L1+L3 Pipe End (Basic Diameter Position) Position away from Pipe End by (L1+L3) Maximum Basic Size of Diameter MaximumValueMinimumValueTolerance MaximumValue MinimumValueTolerance StraightBored HolePositionℓg ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩ ⑪ ⑫ 1/16 - 27 NPT 4.064 2.822 6.886 6.510 6.388 0.122 6.080 5.958 0.122 6.05 12.00 1/8 - 27 NPT 4.102 2.822 6.924 8.857 8.736 0.122 8.425 8.303 0.122 8.39 12.05 1/4 - 18 NPT 5.786 4.234 10.020 11.514 11.357 0.157 10.888 10.730 0.157 10.85 17.45 3/8 - 18 NPT 6.096 4.234 10.330 14.953 14.796 0.157 14.308 14.150 0.157 14.27 17.65 1/2 - 14 NPT 8.128 5.443 13.571 18.485 18.323 0.163 17.637 17.475 0.163 17.60 22.85 3/4 - 14 NPT 8.611 5.443 14.054 23.831 23.668 0.163 22.952 22.790 0.163 22.91 22.95 1 - 11 1/2 NPT 10.160 6.627 16.787 29.868 29.696 0.173 28.819 28.647 0.173 28.78 27.40 1 1/4 - 11 1/2 NPT 10.668 6.627 17.295 38.625 38.452 0.173 37.544 37.372 0.173 37.50 28.10 1 1/2 - 11 1/2 NPT 10.668 6.627 17.295 44.695 44.522 0.173 43.614 43.441 0.173 43.57 28.40 2 - 11 1/2 NPT 11.074 6.627 17.701 56.732 56.560 0.173 55.626 55.454 0.173 55.58 28.00 2 1/2 - 8 NPT 17.323 6.350 23.673 67.806 67.618 0.188 66.326 66.138 0.188 66.28 40.80 3- 8 NPT 19.456 6.350 25.806 83.715 83.527 0.188 82.102 81.914 0.188 82.05 42.95 Remarks 1. Pipe End is Basic Diameter Position (E1). Remarks 2. Effective Thread Length is the length away from Pipe End by (L1+L3). Remarks 3. C o n c e r n i n g bored hole shape, NPT INTERNAL THREAD considering load on taps, taper bored L3 L1 hole is recommended. Remarks 4. When applying taper bored hole, by referring to values in shown columns ⑤ , ⑥ and ⑧ , ⑨ , prepare the taper NPT EXTERNAL THREAD hole by using pipe reamer (1/16 taper). By referring to values shown in 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. Technical-44