Engineering & PLMFree referencePDF, Excel, Word exportDiscrete Manufacturing

Metric Tap Drill and Clearance Hole Size Chart

Pick a metric thread and read the drill size for tapping plus the clearance hole for the mating part. The chart covers the sizes most often used on machined parts and fixtures, in both coarse and common fine pitches.

Download:
ThreadPitch (mm)SeriesTap drill, cut tap (mm)Clearance fine (mm)Clearance medium (mm)Clearance coarse (mm)
M1.6
0.35
Coarse
1.25
1.7
1.8
2
M2
0.4
Coarse
1.6
2.2
2.4
2.6
M2.5
0.45
Coarse
2.05
2.7
2.9
3.1
M3
0.5
Coarse
2.5
3.2
3.4
3.6
M4
0.7
Coarse
3.3
4.3
4.5
4.8
M5
0.8
Coarse
4.2
5.3
5.5
5.8
M6
1
Coarse
5
6.4
6.6
7
M8
1.25
Coarse
6.8
8.4
9
10
M10
1.5
Coarse
8.5
10.5
11
12
M12
1.75
Coarse
10.2
13
13.5
14.5
M14
2
Coarse
12
15
15.5
16.5
M16
2
Coarse
14
17
17.5
18.5
M20
2.5
Coarse
17.5
21
22
24
M24
3
Coarse
21
25
26
28
M30
3.5
Coarse
26.5
31
33
35
M8
1
Fine
7
8.4
9
10
M10
1.25
Fine
8.8
10.5
11
12
M12
1.25
Fine
10.8
13
13.5
14.5
M16
1.5
Fine
14.5
17
17.5
18.5
M20
1.5
Fine
18.5
21
22
24

Tap drill sizes are for cutting taps (nominal diameter minus pitch, rounded to a standard drill). Roll-forming taps need a larger drill, normally close to the pitch diameter, so use the tap maker data for those. Clearance values follow the ISO 273 series.

Hole and thread standards in your ERP

Optional: a short review of how engineering standards could be searchable from your ERP and PLM data.

Optional. The tool and every export work without this. No spam.

How to use the chart

For a tapped hole, read the tap drill column for the thread and pitch you are cutting. The rule behind it is nominal diameter minus pitch, so M8 x 1.25 gives 6.75 mm, rounded to the standard 6.8 mm drill. For the mating part, choose a clearance series: fine for accurately located parts, medium for general work and coarse where alignment is loose, such as sheet metal or weldments. Filter by thread, such as M10, to see coarse and fine options together.

  • Use the fine column when holes are located by a tight position tolerance
  • Use the coarse column when multiple parts must be aligned by hand
  • Export the list to attach to a CNC setup sheet

Thread engagement and drill size

A drill equal to the nominal diameter minus the pitch gives about 75 percent thread height in a cut thread, which is the usual compromise between holding strength and tap load. Going a little larger lowers tap torque in hard alloys and stainless, and reduces broken taps, at the cost of strength. In steel, a thread engagement of about one and a half times the diameter is usually enough to break the bolt before stripping the thread.

Worked example

A bracket needs an M6 screw into aluminum and an M6 clearance hole in the mating plate. The chart gives a 5.0 mm tap drill for the M6 x 1 coarse thread. For the plate, medium clearance is 6.6 mm. If the plate positions a dowel pattern and the screws only clamp, the fine value 6.4 mm gives tighter alignment. Record the callout once in the CAD hole table, so the CNC programmer and the drawing agree.

Common mistakes

The common errors are using a clearance drill size for tapping, mixing coarse and fine pitch tap drills, and applying a cutting tap drill when the operator will use a roll tap. Another is forgetting to deduct the drill point angle when computing tapped depth, so the thread bottoms out. Always call out thread depth and drill depth separately on the drawing.

Frequently Asked Questions

What drill size is used for an M6 tap?

An M6 x 1 coarse thread uses a 5.0 mm drill for a cutting tap. The rule is nominal diameter minus pitch. Roll-forming taps need a larger drill, so check the tap maker table rather than using this figure for them.

What is the clearance hole for M8?

Under ISO 273 the M8 clearance hole is 8.4 mm for fine, 9 mm for medium and 10 mm for coarse. Medium is the usual default for general assembly, and fine is chosen when hole position tolerances are tight.

Does the same table work for fine pitch threads?

The tap drill differs, because the pitch is smaller, so the fine pitch rows give their own drill sizes. The clearance hole for a given diameter is the same for coarse and fine pitch, since it depends on the bolt diameter.

How deep should the drill go for a blind tapped hole?

Drill deeper than the usable thread by at least two to three pitches for a taper or plug tap, and more for a bottoming tap if chips must clear. The drawing should state both the full thread depth and the drill depth.

If your shop keeps hole and thread standards in the ERP item or routing notes, Netray can help make them searchable by a private assistant for engineers and programmers.

Talk to an ExpertExplore More Free Tools

Related Tools

Engineering & PLM

Metric Thread Dimensions and Tensile Stress Area Calculator

Basic and design dimensions for an ISO metric thread plus the tensile stress area and breaking load for a given property class.

Engineering & PLM

ISO 2768-1 General Linear Tolerances Reference

Look up the permitted deviation for any linear dimension, external radius or chamfer under ISO 2768-1 tolerance classes fine, medium, coarse and very coarse.

Engineering & PLM

Design for Manufacturing Tolerance Review Checklist

A pre-release checklist for reviewing tolerances on a drawing for manufacturability, function and inspectability.

Engineering & PLM

Typical Achievable Tolerance by Manufacturing Process Reference

Planning reference of the IT grade and approximate tolerance band each common manufacturing process can hold on a 25 mm feature.

More Engineering & PLM tools

See all
Back to All Tools