Before revision: In mechanical engineering, limits and fits are a set of rules how many thousandths of an inch or Millimetre a part's measurement is to be under or over the theoretical size to achieve various sorts of fit ( sliding fit, rotating fit, non-sliding fit, loose fit, etc.)
After revision: In mechanical engineering, limits and fits are a set of rules regarding the dimensions and tolerances of machined parts if they are to achieve the desired ease of assembly, and security after assembly -interference fit, sliding fit, rotating fit, non-sliding fit, loose fit, etc.)