British & ISO Pipe Threads

  BSPT (Taper) BSPP (Straight) ISO (Taper) ISO (straight)
designation Pipe Size TPI Tap Drill Size Decimal inch Tap Drill Size Decimal inch Tap Drill Size mm Decimal inch Tap Drill Size mm Decimal inch
1/16 - 28   28 1/4 0.2500 F 0.2570 6.3mm 0.2480 6.5mm 0.256
1/8 - 28 6mm 28 21/64 0.3281 Q 0.3320 8.3mm 0.3268 8.5mm 0.335
1/4 - 19 8mm 19 7/16 0.4375 29/64 0.4531 11mm 0.4331 11.5mm 0.453
3/8 - 19 10mm 19 9/16 0.5625 37/64 0.5781 14.5mm 0.5709 15mm 0.591
1/2 - 14 15mm 14 23/32 0.7188 47/64 0.7344 18mm 0.7087 18.5mm 0.728
3/4 - 14 20mm 14 59/64 0.9219 61/64 0.9531 23.5mm 0.9252 24mm 0.945
1 - 11 25mm 11 1 11/64 1.1719 1 3/16 1.1875 29.5mm 1.1614 30.2mm 1.189
1 1/4 - 11 32mm 11 1 1/2 1.5000 1 17/32 1.5313 38mm 1.4961 39mm 1.535
1 1/2 - 11 40mm 11 1 47/64 1.7344 1 49/64 1.7656 44mm 1.7323 45mm 1.772
2-11 50mm 11 2 3/16 2.1875 2 15/64 2.2344 55.5mm 2.1850 56.5mm 2.224

Last Updated: 24 September 2011

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