Metric Thread Dimensions Chart

Frequently asked questions

What does M10 x 1.5 mean?

A metric thread with a 10 mm nominal (major) diameter and a 1.5 mm pitch, the distance from one thread crest to the next. For the coarse series the pitch is usually left off, so plain M10 means M10 x 1.5. Fine pitches are always written out, as in M10 x 1.25.

What tap drill do I use for an M6 thread?

A 5.0 mm drill. The metric rule is tap drill = nominal diameter - pitch, so M6 x 1 takes 6 - 1 = 5.0 mm and M10 x 1.5 takes 8.5 mm. The rule gives roughly 75 to 80 percent thread; where it lands between stock drills, M8 is usually drilled 6.8 mm and M12 10.2 mm.

What is the difference between 6g and 6H?

Both are ISO 965-1 medium tolerance classes. Lowercase letters are external threads and uppercase are internal. 6H holes have no allowance: the smallest pitch diameter is the basic size. 6g bolts sit slightly under basic (about 0.032 mm on an M10 x 1.5), which eases assembly and leaves room for a thin coating. 6H/6g is the normal default fit.

Should I use coarse or fine metric threads?

Use coarse by default: it is faster to tap, less sensitive to damage and every fastener is stocked in it. Choose fine pitch for thin walls, short engagement, fine adjustment, or when you need a bit more tensile stress area and resistance to loosening. Fine-pitch taps and nuts are less common, so check availability first.

How do you calculate the pitch diameter of a metric thread?

d2 = d - 0.649519 x P. For M10 x 1.5 that is 10 - 0.974 = 9.026 mm. The internal minor diameter is d - 1.082532 x P (8.376 mm) and the external minor diameter is d - 1.226869 x P (8.160 mm).