This list includes abbreviations common to the vocabulary of people who work with engineering drawings in the manufacture and inspection of parts and assemblies.
Technical standards exist to provide glossaries of abbreviations, acronyms, and symbols that may be found on engineering drawings.
oc on center On a technical drawing a dimension or note that is given only for reference and therefore is not intended to be used as a part acceptance criterion (although it may be used as an aid to production or inspection).
Parenethesis( value ) denote the same thing and were standardized by ASME.
This rule prevents the mistake of defining it in two different ways accidentally; the "main" (non-reference) mention is the only one that counts as a feature definition and thus as a part acceptance criterion.