Metric Threads

The most commonly used type of general-purpose screw thread, one of the first international standards agreed when the International Organization for Standardization was set up in 1947. Metric threads are becoming more common in model engineering, but there are quite a few applications where other, perhaps better scale threads are still used – see our Threads page for a list of the other forms.

  • BS 919-3:2007 Screw gauge limits and tolerances. Specification for gauges for screw threads of ISO metric form
  • ISO 68-1: ISO general purpose screw threads – Basic profile – Metric screw threads.
  • ISO 261, titled ISO general purpose metric screw threads-General plan, is an international standard that defines a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads.
  • ISO 262, titled ISO general purpose metric screw threads-Selected sizes for screws, bolts and nuts, defines a shorter list of thread dimensions – a subset of the combinations listed in ISO 261
Metric Coarse
Size [mm]Pitch [mm]Tap drill [mm]Clearance drill [mm]
1.00.250.75
1.10.250.85
1.20.250.95
1.40.31.1
1.60.351.251.8
1.70.351.3
1.80.351.45
20.41.62.4
2.20.451.75
2.50.452.052.90
3.00.52.53.40
3.50.62.93.90
4.00.73.34.50
4.50.753.7
50.84.25.50
6156.60
716
81.256.89.0
91.257.8
101.58.512.0
111.59.5
121.7510.214.0
1421216.0
1621418.0
182.515.5
202.517.522.0
222.519.525.0
2432127.0
2732430.0
303.526.533.0
333.529.5
3643240.0
39435

Metric Fine
Size [mm]Pitch [mm]Tap drill [mm]Clearance drill [mm]
4.353.6
4.53.5
5.54.5
6.55.5
6.755.25
7.756.25
8.579
8.757.259
817.59
918
10.759.2511
101911
101.258.811
11110
12.7511.2514
1211114
121.510.514
1411316
141.2512.816
141.512.516
1611518
161.514.518
1811720
1821620
2011922
201.518.522
2021822
2212124
221.520.524
2222024
241.522.526
2422226
261.524.5
271.525.530
2722530
281.526.5
301.528.533
3022833
3323136
3633339
3933642

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