Tapping Drill Size Chart for Thread Cutting Taps (Metric-Imperial Values)

For your convenience, we’ve compiled a simplified chart of tapping coarse and fine drill sizes.

We trust that the information below is self-explanatory and straightforward.

Thread Size Pitch Coarse Drill Size Thread Size (mm) Pitch (mm) Drill Size (mm) Drill Size (inch) Thread Size Coarse Drill Fine Drill Size
Metric (mm) Metric (mm) Metric (mm) Decimal inches (~) Fractional inches (~) #             Metric (mm)
M1.0 0.25 0.75 0.03   #67 M1.0 0.25 0.75 0.03 M1 0.75 ---
M1.2 0.25 0.95 0.037   #61 M1.2 0.25 0.95 0.037 M1.2 0.95 ---
M1.4 0.30 1.10 0.043   #55 M1.4 0.30 1.10 0.043 M1.4 1.1 ---
M1.6 0.35 1.25 0.049 3/64   M1.6 0.35 1.25 0.049 M1.6 1.25 ---
M1.8 0.35 1.45 0.059   #53 M1.8 0.35 1.45 0.057 M1.8 1.45 ---
M2.0 0.40 1.60 0.063   #52 M2.0 0.40 1.60 0.063 M2 1.6 1.75
M2.2 0.45 1.75 0.070   #50 M2.2 0.45 1.75 0.069 --- --- ---
M2.5 0.45 2.05 0.081   #46 M2.5 0.45 2.05 0.081 M2.5 2.05 2.15
M3.0 0.50 2.50 0.098   #37 M3.0 0.50 2.50 0.098 M3 2.5 2.65
M3.5 0.60 2.90 0.114   #32 M3.5 0.60 2.90 0.114 M3.5 2.9 ---
M4.0 0.70 3.30 0.130   #29 M4.0 0.70 3.30 0.13 M4 3.3 3.5
M4.5 0.75 3.70 0.146   #25 M4.5 0.75 3.70 0.146 --- --- ---
M5.0 0.80 4.20 0.165   #16 M5.0 0.80 4.20 0.165 M5 4.2 4.5
M6.0 1.00 5.00 0.197   #8 M6.0 1.00 5.00 0.197 M6 5 5.3
M7.0 1.00 6.00 0.236   B --- ---     M7 6 6.25
M8.0 1.25 6.75 0.268   H M8.0 1.25 6.80 0.268 M8 6.8 7
M9.0 1.25 7.75 0.305   #31 --- ---     --- --- ---
M10.0 1.50 8.50 0.335   R M10.0 1.50 8.50 0.335 M10 8.5 9
M11.0 1.50 9.50 0.374   #9 --- ---     --- --- ---
M12.0 1.75 10.25 0.402   Y M12.0 1.75 10.20 0.402 M12 10.2 10.5
M14.0 2.00 12.00 0.472 15/32   M14.0 2.00 12.00 0.472 M14 12 12.5
M16.0 2.00 14.00 0.551 9/16   M16.0 2.00 14.00 0.551 M16 14 14.5
M18.0 2.50 15.50 0.61 39/64   M18.0 2.50 15.50 0.61 M18 15.5 16.5
M20.0 2.50 17.50 0.689 11/16   M20.0 2.50 17.50 0.689 M20 17.5 18.5
M22.0 2.50 19.50 0.768 49/64   M22.0 2.50 19.50 0.768 M22 19.5 20.5
M24.0 3.00 21.00 0.827 53/64   M24.0 3.00 21.00 0.827 M24 21 22
M27.0 3.00 24.00 0.945 61/64   M27.0 3.00 24.00 0.945 M27 24 ---
M30.0 3.50 26.50 1.043 1-1/16   M30.0 3.50 26.50 1.043 M30 26.5 ---
M33.0 3.50 29.00 1.161 1-1/8   M33.0 3.50 29.50 1.161 M33 --- ---
M36.0 4.00 32.00 1.26 1-1/4   M36.0 4.00 32.00 1.26 M36 32 ---
M39.0 4.00 35.00   1-3/8   --- ---     M39 --- ---
M42.0 4.50 37.50 1.476 1-1/2   M42.0 4.50 37.50 1.476 M42 37.5 ---
M45.0 4.50 40.50 1.594 1-5/8   M45.0 4.50 40.50 1.594 M45 40.5 ---
M48.0 5.00 43.00 1.693 1-3/4   M48.0 5.00 43.00 1.693 M48 43 ---
M50.0 5.00 45.50 1.772 1-7/8   M50.0 5.00 45.00 1.772 M50 --- 48.5

Table values compiled from:

Notes:

  • This table covers a range of sizes but might not include all available thread sizes.
  • Not all metric tapping drill bits have imperial equivalents, and vice versa.
  • Fine thread sizes are less common than coarse threads.
  • Coarse or fine threads require different drill sizes.
  • Some metric values are close enough to essentially have the same imperial counterpart.
  • Some values are rounded to their nearest thousandth millimeters and ten-thousandth decimal inches.

Considerations:

  • The choice of drill size and thread depth can vary significantly based on the material being tapped (eg steel, aluminium, plastic).
  • The desired thread depth affects the necessary clearance for the tap.
  • The tightness of the thread (close, medium, or free fit) influences the drill size.
  • Different tap types (taper, plug, bottoming) require slightly different drill sizes.
  • The Engineers Black Book’s section in calculation of tapping drill sizes advises to “use a good cutting oil or lubricant rather than coolant for fluteless (thread forming) taps”.

Important:

  • Always consult a detailed tap drill chart for accurate and precise drill size selection.

You may want to consider getting the Engineers Black Book (3rd Edition – Metric) for more complete information, specifically:

  • Calculation, formulas and examples of tapping drill size:
    • For thread cutting taps (tapping drill size in metric and inches, thread percentage in metric)
    • For fluteless taps (tapping drill size in metric and inches)
  • Complete and detailed tapping drill sizes (screw size, major/minor/ effective diameters, tap and clearance drill sizes etc) for thread cutting taps in:
    • ISO metric coarse, metric fine, metric conduit, metric special pitches and metric sparkplug
    • UNC (Unified National Coarse)
    • UNF (Unified National Fine)
    • UNEF (Unified National Extra Fine)
    • BA (British Association)
    • BSW (British Standard Whitworth)
    • BSF (British Standard Fine)
    • BSP (British Standard Pipe)
    • BSPT (British Standard Pipe Taper)
    • PG (Panzerrohr-Gewinde)
    • NPT (American National Pipe Taper)