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Metric tap drill sizes M3-M20

Metric tap drill bits define the exact diameter of the pre-drilled hole needed to cut a standard internal thread according to the ISO metric pitch system. The table covers the most commonly used nominal sizes in mechanical engineering, from M3 to M20, and includes standard coarse pitches per ISO 724 / DIN 13-1. Accurate drilling prevents tap breakage, reduces tapping torque, and ensures a complete thread percentage that maintains assembly strength.

Metric Tap Drill Table

Section titled “Metric Tap Drill Table”
Nominal Size Standard Pitch (mm) Tap Drill (mm) Tap Drill (in)
M3 0,5 mm / 0.020 in 2,5 mm 0.0984 in
M4 0,7 mm / 0.028 in 3,3 mm 0.1299 in
M5 0,8 mm / 0.031 in 4,2 mm 0.1654 in
M6 1,0 mm / 0.039 in 5,0 mm 0.1969 in
M8 1,25 mm / 0.049 in 6,75 mm 0.2657 in
M10 1,5 mm / 0.059 in 8,5 mm 0.3346 in
M12 1,75 mm / 0.069 in 10,25 mm 0.4035 in
M14 2,0 mm / 0.079 in 12,0 mm 0.4724 in
M16 2,0 mm / 0.079 in 14,0 mm 0.5512 in
M18 2,5 mm / 0.098 in 15,5 mm 0.6102 in
M20 2,5 mm / 0.098 in 17,5 mm 0.6890 in

Clearance Holes for Metric Bolts (ISO 273)

Section titled “Clearance Holes for Metric Bolts (ISO 273)”
Nominal Size Fine Hole (mm) Fine Hole (in) Medium Hole (mm) Medium Hole (in) Coarse Hole (mm) Coarse Hole (in)
M3 3,2 mm 0.1260 in 3,35 mm 0.1319 in 3,6 mm 0.1417 in
M4 4,3 mm 0.1693 in 4,5 mm 0.1772 in 4,8 mm 0.1890 in
M5 5,3 mm 0.2087 in 5,5 mm 0.2165 in 5,8 mm 0.2283 in
M6 6,4 mm 0.2520 in 6,5 mm 0.2559 in 7,0 mm 0.2756 in
M8 8,4 mm 0.3307 in 9,0 mm 0.3543 in 10,0 mm 0.3937 in
M10 10,5 mm 0.4134 in 11,0 mm 0.4331 in 12,0 mm 0.4724 in
M12 13,0 mm 0.5118 in 14,0 mm 0.5512 in 15,0 mm 0.5906 in
M14 15,0 mm 0.5906 in 16,0 mm 0.6299 in 17,0 mm 0.6693 in
M16 17,0 mm 0.6693 in 18,0 mm 0.7087 in 19,0 mm 0.7480 in
M18 19,0 mm 0.7480 in 20,0 mm 0.7874 in 22,0 mm 0.8661 in
M20 21,0 mm 0.8268 in 22,0 mm 0.8661 in 24,0 mm 0.9449 in
Section titled “Recommended Tightening Torque (Grade 8.8, Dry)”
Nominal Size Torque (N·m) Torque (ft·lb)
M3 0,5 N·m 0,4 ft·lb
M4 1,1 N·m 0,8 ft·lb
M5 2,2 N·m 1,6 ft·lb
M6 3,8 N·m 2,8 ft·lb
M8 9,5 N·m 7,0 ft·lb
M10 19,5 N·m 14,4 ft·lb
M12 34,0 N·m 25,1 ft·lb
M14 54,0 N·m 39,8 ft·lb
M16 84,0 N·m 62,0 ft·lb
M18 116,0 N·m 85,6 ft·lb
M20 164,0 N·m 121 ft·lb

Allowable Loads and Mechanical Properties of Metric Bolts Grade 8.8

Section titled “Allowable Loads and Mechanical Properties of Metric Bolts Grade 8.8”
Nominal Size Tensile Stress Area (mm²) Tensile Stress Area (in²) Proof Load (kN) Proof Load (lbf) Ultimate Tensile Strength (kN) Ultimate Tensile Strength (lbf)
M3 5,03 mm² 0.00780 in² 4,0 kN 900 lbf 6,4 kN 1440 lbf
M4 8,78 mm² 0.01361 in² 7,8 kN 1750 lbf 12,6 kN 2830 lbf
M5 14,2 mm² 0.0220 in² 12,5 kN 2810 lbf 20,0 kN 4500 lbf
M6 20,1 mm² 0.0312 in² 18,6 kN 4180 lbf 30,0 kN 6740 lbf
M8 36,6 mm² 0.0567 in² 33,8 kN 7600 lbf 54,5 kN 12250 lbf
M10 58,0 mm² 0.0899 in² 53,6 kN 12050 lbf 86,5 kN 19450 lbf
M12 84,3 mm² 0.1307 in² 77,9 kN 17520 lbf 126 kN 28330 lbf
M14 115 mm² 0.1783 in² 106 kN 23830 lbf 172 kN 38670 lbf
M16 157 mm² 0.2434 in² 145 kN 32630 lbf 234 kN 52650 lbf
M18 192 mm² 0.2976 in² 177 kN 39780 lbf 286 kN 64300 lbf
M20 245 mm² 0.3798 in² 226 kN 50800 lbf 365 kN 82050 lbf

Standard Equivalences (DIN, ISO, ANSI)

Section titled “Standard Equivalences (DIN, ISO, ANSI)”

The coarse metric threads used in this reference conform to the unified profile defined by ISO 724 – Metric screw thread of general use – Basic dimensions. The German standard DIN 13-1 is dimensionally identical to ISO 724 for coarse pitch threads, so the drill, nominal diameter, and pitch data are interchangeable. In the North American sphere, the metric series is covered by ANSI/ASME B1.13M, which adopts the same thread profile (60°) and the same tolerances. There is no technical difference between a tapped hole according to DIN and ISO; both require the same drill diameter before tapping. The clearance hole table follows ISO 273 – Clearance holes for bolts – which establishes the fine, medium, and coarse series, equivalent to assembly tolerances H12, H13, and H14 respectively.

Frequently Asked Questions (FAQ)

Section titled “Frequently Asked Questions (FAQ)”

What is the correct drill bit for tapping an M12 x 1.75 hole?

Section titled “What is the correct drill bit for tapping an M12 x 1.75 hole?”

A 10,25 mm / 0.4035 in drill is required for the M12 coarse pitch tap. This value results from subtracting the pitch from the nominal diameter (12 – 1,75 = 10,25 mm) and produces a thread percentage close to 77 %, the optimal balance between strength and tapping torque.

What torque should be used to tighten a grade 8.8 M8 bolt dry?

Section titled “What torque should be used to tighten a grade 8.8 M8 bolt dry?”

The maximum recommended tightening torque for a grade 8.8 M8 bolt assembled dry is 9,5 N·m / 7,0 ft·lb. This value is based on an approximate friction coefficient of μ = 0,14 and generates a preload of about 80 % of the bolt’s yield strength.

What allowable tensile load can a grade 8.8 M16 bolt withstand?

Section titled “What allowable tensile load can a grade 8.8 M16 bolt withstand?”

The proof load (90 % of the yield strength) for an M16 grade 8.8 is approximately 91,0 kN / 20460 lbf. For design calculations, an additional safety factor of 1.5 to 2 is usually applied to this value.

Is there a difference between DIN 13 and ISO 724 for coarse metric threads?

Section titled “Is there a difference between DIN 13 and ISO 724 for coarse metric threads?”

Both specify the same 60° thread profile and the same basic dimensions (major diameter, pitch, pitch diameter). They are dimensionally interchangeable; the differences are limited to the presentation of tolerances, which in any case do not affect the drill size.

What is the standard pitch of an M20 bolt?

Section titled “What is the standard pitch of an M20 bolt?”

The standard coarse pitch for M20 is 2,5 mm / 0.0984 in. Fine pitches exist (M20 x 2,0, x 1,5, x 1,0) but the common drill table refers to the coarse pitch.

Which imperial drill bit is closest to the one needed for an M10 x 1.5 tap?

Section titled “Which imperial drill bit is closest to the one needed for an M10 x 1.5 tap?”

The 11/32 in drill equals 8,73 mm, while the recommended size is 8,50 mm / 0.3346 in; the 11/32 in slightly oversizes the hole. The direct metric option (8,5 mm) provides a higher thread percentage and is preferred whenever available.

References

Section titled “References”