Subject:- Metrology and Quality Engineering

Topic:- Introduction to Metrology

Difficulty:- Low

Grades of Tolerance:-

It is an indication of the level of accuracy. There are 18 grades of tolerances – IT01, IT0, IT1 to IT16 IT01 to IT4 - For production of gauges, plug gauges, measuring instruments, IT5 to IT 7 - For fits in precision engineering applications IT8 to IT11 – For General Engineering IT12 to IT14–For Sheet metal working or press working IT15 to IT16 – For processes like casting, general cutting work.

Standard Tolerance: Various grades of tolerances are defined using the ‘standard tolerance unit’, (i) in micrometer, which is a function of basic size

where, D (mm) is the geometric mean of the lower and upper diameters of a particular diameter step within which the chosen the diameter D lies. Diameter steps in I.S.I are: (a-b, where a is above and b is up to, Refer Table in the following sheet)