3/8-32 tap drill size

    Use a 11/32 drill (0.3438 in) for a 3/8-32 cutting tap at 75% thread.

    Drills for 3/8-32 (UNEF)
    Tap typeDrillDecimal (in)
    Cutting tap, 75% thread11/320.3438
    Cutting tap, 50% thread (hard material)T0.3580
    Roll / form tap, 65% thread23/640.3594
    Pitch
    0.7938 mm (32 TPI)
    Major Ø
    0.3750
    Pitch Ø
    0.3547
    Minor Ø
    0.3412

    3/8-32 tapping speeds and feeds

    Feed = pitch (0.0313 in per rev). Starting points for a general-purpose HSS cut tap:

    • Aluminum 6061 / 7075: 710 RPM · 22.2 IPM
    • Free-machining / mild steel: 200 RPM · 6.25 IPM
    • 304 / 316 stainless: 100 RPM · 3.13 IPM

    Tap speeds and feeds by size · 11/32 drill size and speeds

    Open the tap drill calculatorRoll tap chartHelicoil chart

    Common questions

    What size drill for a 3/8-32 tap?
    Use a 11/32 drill (0.3438 in) for a 3/8-32 cutting tap at 75% thread.
    What drill for a 3/8-32 roll (form) tap?
    About 0.3612 in; the nearest standard drill is 23/64. Check your tap maker's table.

    Other UNEF sizes

    Drill sizes from Machinery's Handbook and ASME B1.1/B1.13M; roll tap sizes from the form-tap formula. Tap and insert makers' tables are authoritative.

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