ISO Metric

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 Organization for Standardization was set up in 1947.Most industrialized countries have long recognized the necessity, and advantage, of adopting the metric system of measurement-or to give it its official title, the International System of Units (SI, for short-derived from its French title, Système international d’unités), which ISO (the International Organization for Standardization) is responsible for maintaining.

ISO metric screw thread

A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D. 

Some important notes from ISO metric screw threads standards:

  • External Screw Thread Designation: Nominal Diameter x Pitch – Tolerance class for pitch diameter – Tolerance class for major diameter (M10 x 1 5g 6g)
  • Internal Screw Thread Designation: – Nominal Diameter x Pitch – Tolerance class for pitch diameter – Tolerance class for minor diameter (M10 x 1 5H 6H)
  • If the two class designations for the pitch diameter and crest diameter are the same it is not necessary to repeat the symbols. (M10 x 1 6g)

– According to ISO 1:2002 , standard reference temperature for geometrical product specification is 20  °C.

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