1-1/8-12 tap drill size

    Use a 1-3/64 drill (1.0469 in) for a 1-1/8-12 cutting tap at 75% thread.

    Drills for 1-1/8-12 (UNF)
    Tap typeDrillDecimal (in)
    Cutting tap, 75% thread1-3/641.0469
    Cutting tap, 50% thread (hard material)1-5/641.0781
    Roll / form tap, 65% thread1-3/321.0938
    Pitch
    2.1167 mm (12 TPI)
    Major Ø
    1.1250
    Pitch Ø
    1.0709
    Minor Ø
    1.0348

    1-1/8-12 tapping speeds and feeds

    Feed = pitch (0.0833 in per rev). Starting points for a general-purpose HSS cut tap:

    • Aluminum 6061 / 7075: 240 RPM · 20.0 IPM
    • Free-machining / mild steel: 70 RPM · 5.83 IPM
    • 304 / 316 stainless: 30 RPM · 2.50 IPM

    1-1/8-12 tap speeds and feeds: all materials, form taps and G84 code

    Open the tap drill calculatorRoll tap chartHelicoil chart

    Common questions

    What size drill for a 1-1/8-12 tap?
    Use a 1-3/64 drill (1.0469 in) for a 1-1/8-12 cutting tap at 75% thread.
    What drill for a 1-1/8-12 roll (form) tap?
    About 1.0882 in; the nearest standard drill is 1-3/32. Check your tap maker's table.

    Other UNF 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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