15. Bored hole size before tapping ( for thread cutting ) Production data ■ 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 Tap (reference) Size L1 L3 L1+L3 Pipe End (Basic Diameter Position) Position away from Pipe End by Maximum Basic (L1+L3) Size of Diameter Maximum Minimum Tolerance Maximum Minimum Tolerance Straight Position Value Value Value Value Bored Hole ℓg ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩ ⑪ ⑫ NPT 1/16 - 27 4.064 2.822 6.886 6.510 6.388 0.122 6.080 5.958 0.122 6.05 12.00 NPT 1/8 - 27 4.102 2.822 6.924 8.857 8.736 0.122 8.425 8.303 0.122 8.39 12.05 NPT 1/4 - 18 5.786 4.234 10.020 11.514 11.357 0.157 10.888 10.730 0.157 10.85 17.45 NPT 3/8 - 18 6.096 4.234 10.330 14.953 14.796 0.157 14.308 14.150 0.157 14.27 17.65 NPT 1/2 - 14 8.128 5.443 13.571 18.485 18.323 0.163 17.637 17.475 0.163 17.60 22.85 NPT 3/4 - 14 8.611 5.443 14.054 23.831 23.668 0.163 22.952 22.790 0.163 22.91 22.95 NPT 1 - 11.5 10.160 6.627 16.787 29.868 29.696 0.173 28.819 28.647 0.173 28.78 27.40 NPT 1 1/4 - 11.5 10.668 6.627 17.295 38.625 38.452 0.173 37.544 37.372 0.173 37.50 28.10 NPT 1 1/2 - 11.5 10.668 6.627 17.295 44.695 44.522 0.173 43.614 43.441 0.173 43.57 28.40 NPT 2 - 11.5 11.074 6.627 17.701 56.732 56.560 0.173 55.626 55.454 0.173 55.58 28.00 Remarks 1. Pipe End is Basic Diameter Position (E1). NPT INTERNAL THREAD Remarks 2. Effective Thread Length is the length away from L3 L1 Pipe End by (L1+L3). Remarks 3. Concerning bored hole shape, considering load on taps, taper bored hole is recommended. NPT EXTERNAL THREAD Remarks 4. When applying taper bored hole, by referring to values in shown columns ⑤, ⑥ and ⑧, ⑨, E3 E0 E1 D prepare the taper 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 Information Technical-43 814