3-4 tap drill size

    Use a 2-3/4 drill (2.7500 in) for a 3-4 cutting tap at 75% thread.

    Drills for 3-4 (UNC)
    Tap typeDrillDecimal (in)
    Cutting tap, 75% thread2-3/42.7500
    Cutting tap, 50% thread (hard material)2-27/322.8438
    Roll / form tap, 65% thread2-7/82.8750
    Pitch
    6.35 mm (4 TPI)
    Major Ø
    3.0000
    Pitch Ø
    2.8376
    Minor Ø
    2.7294
    Open the tap drill calculatorRoll tap chartHelicoil chart

    Common questions

    What size drill for a 3-4 tap?
    Use a 2-3/4 drill (2.7500 in) for a 3-4 cutting tap at 75% thread.
    What drill for a 3-4 roll (form) tap?
    About 2.8895 in; the nearest standard drill is 2-7/8. Check your tap maker's table.

    Other UNC 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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