24. Drill size and recommended hole size for cutting taps Intro American Taper Pipe Threads (NPT) (Refer to ANSI/ASME B1.20.1-1983) Unit: mm SP Minor Diameter Bored Hole Size reference(reference)Tap Size L1 L3 L1+L3 Pipe End (Basic Diameter Position) Position away from Pipe End by (L1+L3) Maximum Size Basic Diameter MaximumValueMinimumValue Tolerance MaximumValueMinimumValueTolerance of StraightBored HolePositionℓg SL 1 2 3 4 5 6 7 8 9 0 ! " 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 0.121 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 0.158 10.85 17.45 PO NPT 3/8 - 18 6.096 4.234 10.330 14.953 14.796 0.157 14.308 14.150 0.158 14.27 17.65 NPT 1/2 - 14 8.128 5.443 13.571 18.485 18.323 0.162 17.637 17.475 0.162 17.60 22.85 NPT 3/4 - 14 8.611 5.443 14.054 23.831 23.668 0.163 22.952 22.790 0.162 22.91 22.95 NPT 1 - 11.5 10.160 6.627 16.787 29.868 29.696 0.172 28.819 28.647 0.172 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 0.172 37.50 28.10 ST 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 0.172 55.626 55.454 0.172 55.58 28.00 NPT 2 1/2 - 8 17.323 6.350 23.673 67.806 67.618 0.188 66.326 66.138 0.188 66.28 40.80 NPT 3-8 19.456 6.350 25.806 83.715 83.527 0.188 82.102 81.914 0.188 82.05 42.95 ROLL CARBIDE LONG 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 HAND on taps, taper bored hole is recommended. TAPS NPT EXTERNAL THREAD Remarks 4. When applying taper bored hole. by referring to values in shown columns 5, 6 and 8, 9, prepare the taper hole by using pipe reamer (1/16 taper). By referring to values shown in EG (STI) column !, select the drill diameter beforereaming by taking reamer's margin into account. Remarks 5. When preparing straight bored hole, by referring to values shown in column !, select drill SPECIAL diameter. THREADS, GAUGES THREAD MILLS DIES CENTER DRILLS Technical info 722 E3 E0 E1 D