Tap Drill Chart

The tap drill for a 60° thread is tap drill = major − (%thread × pitch) ÷ 76.98. This chart lists the drill size at 75% engagement (the traditional default) and at 65% (which taps far more easily for almost the same strength), plus each thread's major diameter, pitch and 100%-form minor diameter.

Rows

Columns

Basis

ISO 261 / ISO 262 / ASME B1.1

Reviewed

June 1, 2026

Use the nearest available drill at or just above the listed size. Going under raises tapping torque and tap-breakage risk sharply for little extra strength, so 65% is a safe everyday choice; reserve 75%+ for thin or soft sections. For a thread or engagement not listed, use the calculator.

Tap drill sizes by thread and engagement.

Thread

Major Ø (mm)

Pitch (mm)

Tap drill @75% (mm)

Tap drill @65% (mm)

Minor Ø (mm)

0.5

2.51

2.58

2.46

0.7

3.32

3.41

3.24

0.8

4.22

4.32

4.13

5.03

5.16

4.92

1.25

6.78

6.94

6.65

M10

1.5

8.54

8.73

8.38

M12

1.75

10.3

10.5

10.1

M16

14.1

14.3

13.8

M20

2.5

17.6

17.9

17.3

M24

21.1

21.5

20.8

M8x1

7.03

7.16

6.92

M10x1.25

1.25

8.78

8.94

8.65

M12x1.25

1.25

10.8

10.9

10.6

#10-24 UNC

4.826

1.0583

3.79

3.93

3.68

1/4-20 UNC

6.35

1.27

5.11

5.28

4.98

5/16-18 UNC

7.9375

1.4111

6.56

6.75

6.41

3/8-16 UNC

9.525

1.5875

7.98

8.18

7.81

1/2-13 UNC

12.7

1.9538

10.8

11.1

10.6

1/4-28 UNF

6.35

0.9071

5.47

5.58

5.37

3/8-24 UNF

9.525

1.0583

8.49

8.63

8.38