M6 coarse pitch is 1 mm. Basic pitch diameter 5.35 mm, external minor diameter 4.773 mm, and a 5 mm tap drill. Fine pitches of 0.75 mm are also tabulated.
M6 is an ISO metric thread on the 60° basic profile, so every dimension below follows from two numbers: the 6 mm nominal diameter and the 1 mm coarse pitch. Drawings that call up M6 without a pitch mean the coarse series unless the note says otherwise.
Basic profile dimensions to ISO 68-1, with the tap drill for standard thread engagement.
Pitch diameter and minor diameters are derived from the ISO 68-1 basic profile (d2 = d − 0.649519P, d3 = d − 1.226869P, D1 = d − 1.082532P). The tap drill is the arithmetic d − P for 75-80% thread engagement; pick the nearest drill in the preferred series, which is why published charts quote 5 mm for some sizes and the adjacent tenth for others.
Fine series for the same nominal diameter. A fine pitch has a larger minor diameter than coarse at the same nominal size, so a gauge for one will not check the other.
| Designation | Pitchmm | Pitch Ømm | Minor Ø ext.mm | Minor Ø int.mm | Tap drillmm |
|---|---|---|---|---|---|
| M6x0.75 | 0.75 | 5.513 | 5.08 | 5.188 | 5.25 |
A standard M6 hexagon head or nut takes a 10 mm across-flats spanner under ISO 272.
An M6 internal thread is checked with a thread plug gauge: a matched GO / NO-GO pair on one handle. The GO end checks the minimum material limit and must enter the full thread by hand; the NO-GO end checks the maximum material limit and must not enter. Because the two ends are cut and lapped as a pair, the setting between them is preserved when the gauge is reconditioned — which is what keeps a working gauge useful after years of use.
External M6 threads are checked with a thread ring gauge or a snap gauge, and setting plugs are used to keep those rings in calibration. The pitch diameter above (5.35 mm) is the dimension being controlled; the major and minor diameters only matter as clearance.
Full coarse and fine series on the metric thread pitch chart, adopted in India as IS 919 / IS 4218.