The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organisation  (ISO) for Standardisation was set up in 1947.

The “M” designation for metric screws indicates the nominal outer diameter of the screw, in millimetres (mm) e.g., an M6 screw has a nominal outer diameter of 6mm.

Standard Metric Threads have a angle of 60° By definition standard Metric thread are Coarse. Metric threads are also available in Fine. For a example a thread specified as M10 would be standard Coarse with a pitch of 1.5mm. On occasions there may be a requirement for a finer pitch thread with the same diameter therefore the thread would be specified as M10x1.0 the (x1.0) being the pitch.

Metric Thread Nomenclature

 

Metric thread Specification & Call-outs (See the Video)