What does the M in a metric thread mean?

The M designates an ISO metric thread, and the number that follows is the nominal outside (major) diameter in millimetres. M6 means a 6 mm nominal diameter thread.

What is thread pitch?

Pitch is the distance in millimetres between two adjacent thread crests. M6 coarse has a 1.0 mm pitch, so the thread advances 1 mm per turn.

What is the difference between coarse and fine threads?

Coarse threads are the default ISO pitch for a size and are faster to assemble and more tolerant of damage. Fine threads have a smaller pitch, giving more holding strength, finer adjustment, and better resistance to vibration.

How do I calculate the tap drill size for a metric thread?

A common rule of thumb for ISO coarse threads is tap drill diameter = nominal diameter minus pitch. For M6 x 1.0 that is 6 - 1 = 5.0 mm, which yields roughly 75 percent thread engagement, the practical target that balances strength against tapping torque.

What is the pitch diameter of a metric thread?

Pitch diameter (d2) is the diameter of an imaginary cylinder where the thread groove and ridge are equal in width. For a 60-degree ISO thread it equals the major diameter minus 0.6495 times the pitch.

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Reference

Metric Thread Pitch Chart

ISO metric thread dimensions for M1–M30: coarse and fine pitch, pitch diameter, minor diameter, and tap drill size. Pick a size to look it up instantly.

Size

Pitch (mm)

Coarse thread chart (M1–M30)