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ISO Metric Screw Thread Tolerances

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The International Organization for Standardization (ISO) set the standard for limits of metric screw thread.  ISO 965 specifies the basic profile for ISO general purpose metric screw threads (M) conforming to ISO 261.

The information below can be used to calculate the values of thread tolerances defined by ISO 965/1.  Screw threads are usually signified by two tolerances. One is for the maximum outside diameter, measured from the major diameter of the thread, and the other is for the pitch diameter, measured from the midpoint of each tooth.

Dimensions in millimetres (mm). Tolerances 6g (6h).  For guidance only.

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