13/16-20 tap drill size

    Use a 49/64 drill (0.7656 in) for a 13/16-20 cutting tap at 75% thread.

    Drills for 13/16-20 (UNEF)
    Tap typeDrillDecimal (in)
    Cutting tap, 75% thread49/640.7656
    Cutting tap, 50% thread (hard material)25/320.7813
    Roll / form tap, 65% thread51/640.7969
    Pitch
    1.27 mm (20 TPI)
    Major Ø
    0.8125
    Pitch Ø
    0.7800
    Minor Ø
    0.7584

    13/16-20 tapping speeds and feeds

    Feed = pitch (0.0500 in per rev). Starting points for a general-purpose HSS cut tap:

    • Aluminum 6061 / 7075: 330 RPM · 16.5 IPM
    • Free-machining / mild steel: 90 RPM · 4.50 IPM
    • 304 / 316 stainless: 50 RPM · 2.50 IPM

    Tap speeds and feeds by size · 49/64 drill size and speeds

    Open the tap drill calculatorRoll tap chartHelicoil chart

    Common questions

    What size drill for a 13/16-20 tap?
    Use a 49/64 drill (0.7656 in) for a 13/16-20 cutting tap at 75% thread.
    What drill for a 13/16-20 roll (form) tap?
    About 0.7904 in; the nearest standard drill is 51/64. 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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