Pipe tap drill chart (NPT, NPTF, BSPT)

    Tap drills for taper pipe threads when you tap without a taper reamer. NPTF dryseal threads usually take a slightly larger drill than NPT in the same size; BSPT uses a 55° Whitworth form and different pitches.

    Open calculatorDownload data (JSON)
    Pipe tap drills without reaming
    SizeTypeTPITap drillInchmm
    1/16NPT27D0.24606.25
    1/8NPT27Q0.33208.43
    1/4NPT187/160.437511.11
    3/8NPT189/160.562514.29
    1/2NPT1445/640.703117.86
    3/4NPT1429/320.906223.02
    1NPT11.51-9/641.140628.97
    1-1/4NPT11.51-31/641.484437.70
    1-1/2NPT11.51-47/641.734444.05
    2NPT11.52-13/642.203155.96
    2-1/2NPT82-5/82.625066.68
    3NPT83-1/43.250082.55
    3-1/2NPT83-3/43.750095.25
    4NPT84-1/44.2500107.95
    1/16NPTF27D0.24606.25
    1/8NPTF27R0.33908.61
    1/4NPTF187/160.437511.11
    3/8NPTF1837/640.578114.68
    1/2NPTF1445/640.703117.86
    3/4NPTF1459/640.921923.42
    1NPTF11.51-5/321.156229.37
    1-1/4NPTF11.51-1/21.500038.10
    1-1/2NPTF11.51-47/641.734444.05
    2NPTF11.52-7/322.218856.36
    2-1/2NPTF82-39/642.609466.28
    3NPTF83-15/643.234482.15
    3-1/2NPTF83-3/43.750095.25
    4NPTF84-1/44.2500107.95
    1/8NPS27S0.34808.84
    1/4NPS1829/640.453111.51
    3/8NPS1819/320.593815.08
    1/2NPS1447/640.734418.65
    3/4NPS1415/160.937523.81
    1NPS11.51-3/161.187530.16
    1-1/4NPS11.51-33/641.515638.50
    1-1/2NPS11.51-3/41.750044.45
    2NPS11.52-7/322.218856.36
    2-1/2NPS82-21/322.656267.47
    3NPS83-9/323.281283.34
    3-1/2NPS83-25/323.781296.04
    4NPS84-9/324.2812108.74
    1/8BSPT288.4 mm (21/64)0.32818.40
    1/4BSPT1911.2 mm (7/16)0.437511.20
    3/8BSPT1914.75 mm (37/64)0.578114.75
    1/2BSPT1418.25 mm (23/32)0.718818.25
    3/4BSPT1423.75 mm (15/16)0.937523.75
    1BSPT1130 mm (1-11/64)1.171930.00
    1-1/4BSPT1138.5 mm (1-33/64)1.515638.50
    1-1/2BSPT1144.5 mm (1-3/4)1.750044.50
    2BSPT1156 mm (2-3/16)2.187556.00
    2-1/2BSPT11Bore to ~72.226 mm (D1 at gauge plane)2.843572.23
    3BSPT11Bore to ~84.926 mm (D1 at gauge plane)3.343584.93
    4BSPT11Bore to ~110.072 mm (D1 at gauge plane)4.3335110.07
    1/16BSPP28G0.26106.63
    1/8BSPP2811/320.34388.73
    1/4BSPP1929/640.453111.51
    3/8BSPP1919/320.593815.08
    1/2BSPP143/40.750019.05
    5/8BSPP1453/640.828121.03
    3/4BSPP1431/320.968824.61
    7/8BSPP141-7/641.109428.18
    1BSPP111-13/641.203130.56
    1-1/4BSPP111-35/641.546939.29
    1-1/2BSPP111-25/321.781245.24
    1-3/4BSPP1122.000050.80
    2BSPP112-1/42.250057.15
    2-1/2BSPP11Bore to ~72.226 mm (D1)2.843572.23
    3BSPP11Bore to ~84.926 mm (D1)3.343584.93
    3-1/2BSPP11Bore to ~97.372 mm (D1)3.833597.37
    4BSPP11Bore to ~110.072 mm (D1)4.3335110.07

    NPT and NPTF: Tapco pipe tap chart (NPT cross-checked with OSG). BSPT: ISO 7-1 charts (ring-plug gage data, FWB, Allied Machine).

    Common questions

    What tap drill for 1/8 NPT?
    Q (0.332 in) for NPT; R (0.339 in) is common for 1/8 NPTF dryseal.
    What tap drill for 1/4 BSPT?
    11.2 mm (7/16 in).
    Can I use an NPT tap for BSPT?
    No. BSPT has a 55° thread angle and 19 TPI at 1/4, versus 60° and 18 TPI for NPT.

    Calculators that use this data

    Drill Chart & Size FinderFractional, number, letter and metric drills with decimal equivalents and a nearest-drill finder.Tap Drill ChartRecommended tap drill sizes for UNC, UNF, and metric threads.

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