If you are a supplier or manufacturer working with parts specified under MS81-2021, ensure you have the correct revision of the PDF. Differences between "Revision 1" and "Revision 2" can lead to significant manufacturing errors, especially when transitioning from old "Class 1/2" systems to the current "f/m/c" classes.
: On older technical drawings, you may see references to "1st Class" or "2nd Class" tolerances. Under modern enforcement, these older designations are often mapped to the Annex MS81-2021 requirements. Key Technical Specifications Ms81-2021 Standard Pdf
According to the Standard Drawing Format, the tolerance should be clearly designated in the title block of the engineering drawing. A typical callout would look like: If you are a supplier or manufacturer working
The standard provides specific millimeter (mm) deviation limits based on the nominal length of the part and its chosen tolerance class. Nominal Dimension (mm) m (Medium) c (Coarse) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Industry Context and Related Standards Under modern enforcement, these older designations are often
: The standard class used for most general machining. c (Coarse) : For parts where precision is less critical.
: This standard applies to machining dimensions of less than 2000 mm for individual machining work.