Editing Engineering tolerance (section)

===International Tolerance grades===
{{main|IT Grade}}
When designing mechanical components, a system of standardized tolerances called '''International Tolerance grades''' are often used. The standard (size) tolerances are divided into two categories: hole and shaft. They are labelled with a letter (capitals for holes and lowercase for shafts) and a number. For example: H7 (hole, [[tap and die#Machine tapping|tapped hole]], or [[nut (hardware)|nut]]) and h7 (shaft or bolt). H7/h6 is a very common standard tolerance which gives a tight fit. The tolerances work in such a way that for a hole H7 means that the hole should be made slightly larger than the base dimension (in this case for an ISO fit 10+0.015−0, meaning that it may be up to 0.015&nbsp;mm larger than the base dimension, and 0&nbsp;mm smaller). The actual amount bigger/smaller depends on the base dimension. For a shaft of the same size, h6 would mean 10+0−0.009, which means the shaft may be as small as 0.009&nbsp;mm smaller than the base dimension and 0&nbsp;mm larger. This method of standard tolerances is also known as Limits and Fits and can be found in [http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=45975&ICS1=17&ICS2=40&ICS3=10 ISO 286-1:2010 (Link to ISO catalog)].

The table below summarises the International Tolerance (IT) grades and the general applications of these grades:

{| class="wikitable" style="text-align:center; margin: 1em auto 1em auto"
|width=70|&nbsp;
|colspan=9|Measuring Tools
|colspan=7|Material
|colspan=5|&nbsp;
|-
!IT Grade
!width=25|01
!width=25|0
!width=25|1
!width=25|2
!width=25|3
!width=25|4
!width=25|5
!width=25|6
!width=25|7
!width=25|8
!width=25|9
!width=25|10
!width=25|11
!width=25|12
!width=25|13
!width=25|14
!width=25|15
!width=25|16
|-
|colspan=7|&nbsp;
|colspan=7|Fits
|colspan=5|Large Manufacturing Tolerances
|}

An analysis of fit by [[statistical interference]] is also extremely useful: It indicates the frequency (or probability) of parts properly fitting together.