IT Grade

IT grade(s) refer to an internationally accepted code system for tolerances on linear dimensions. Such code systems may be used to produce interchangeable parts. In engineering, the word "tolerance" refers to a range of allowable dimensions or values. Standard tolerance grades are a group of tolerances for linear sizes characterized by a common identifier. For SI measurements, a system of tolerance grades defined in ISO 286 is frequently used and identified by the letters IT followed by a number specifying how precise the requirements are, relative to the "nominal size" of a part. 
For example, IT14 refers to a group of tolerances used in manufacturing. For a part dimensioned at 10 mm, IT14 allows for up to 0.36 mm of variation in size. As the IT grade number increases, the tolerances increase; similarly, for larger nominal sizes, the standard tolerances increase. For a part dimensioned at 100 mm, IT14 allows for up to 0.87 mm of variation in size. 
Definition.
The ISO 286 defines the international tolerances grades for nominal sizes up to 3.15 meters as follows:
! colspan = 4 scope = "col" | Nominal size
! colspan = 40 scope = "col" | International tolerance grade
! colspan = 2 scope = "col" | > 
! colspan = 2 scope = "col" | ≤ 
! colspan = 2 scope = "col" | IT01 
! colspan = 2 scope = "col" | IT0 
! colspan = 2 scope = "col" | IT1
! colspan = 2 scope = "col" | IT2
! colspan = 2 scope = "col" | IT3
! colspan = 2 scope = "col" | IT4
! colspan = 2 scope = "col" | IT5
! colspan = 2 scope = "col" | IT6
! colspan = 2 scope = "col" | IT7
! colspan = 2 scope = "col" | IT8
! colspan = 2 scope = "col" | IT9
! colspan = 2 scope = "col" | IT10
! colspan = 2 scope = "col" | IT11
! colspan = 2 scope = "col" | IT12
! colspan = 2 scope = "col" | IT13
! colspan = 2 scope = "col" | IT14
! colspan = 2 scope = "col" | IT15
! colspan = 2 scope = "col" | IT16
! colspan = 2 scope = "col" | IT17
! colspan = 2 scope = "col" | IT18
! colspan = 4 scope = "col" | mm
! colspan = 26 scope = "col" | tolerance in μm 
! colspan = 14 scope = "col" | tolerance in mm 