IT Grade
Encyclopedia
IT Grade refers to the International Tolerance Grade of an industrial process defined in ISO 286. This grade identifies what tolerances a given process can produce for a given dimension.
The specific Tolerance for a particular IT grade is calculated via the following formula:
where:
One thinks of
as being the key dimension on the part and 
as being the required tolerance on that key dimension. The larger the ITG, the looser the tolerance.
has an IT Grade of 13 and a part needs an IT Grade of 5, one cannot injection mold that part to those specifications. It is useful in determining the processes capable of producing parts to the needed specification.
The specific Tolerance for a particular IT grade is calculated via the following formula:
where:
- T is the tolerance in micrometres [µm]
- D is the geometric meanGeometric meanThe geometric mean, in mathematics, is a type of mean or average, which indicates the central tendency or typical value of a set of numbers. It is similar to the arithmetic mean, except that the numbers are multiplied and then the nth root of the resulting product is taken.For instance, the...
dimension in millimeters [mm] - ITG is the IT Grade, a positive integer.
One thinks of
as being the key dimension on the part and as being the required tolerance on that key dimension. The larger the ITG, the looser the tolerance.Meaning and interpretation
An industrial process has an IT Grade associated with, indicating how precise it is. When designing a part, an engineer will typically determine a key dimension (D) and some tolerance (T) on that dimension. Using this formula, the engineer can determine what IT Grade is necessary to produce the part with those specifications. Thus, if injection moldingInjection molding
Injection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity...
has an IT Grade of 13 and a part needs an IT Grade of 5, one cannot injection mold that part to those specifications. It is useful in determining the processes capable of producing parts to the needed specification.
Alternate formulation
The following has been proposed by an unsigned user, though no source is given. In "Manufacturing Processes II" (Tata McGraw-Hill Education) by H S Bawa, the following Equation is given on Page 95 for sizes over 500 mm:| ITG | IT5 | IT6 | ... | IT17 | IT18 |
|---|---|---|---|---|---|
| k | 7 | 10 | ... | 1600 | 2500 |
See also
- TolerancesTolerance (engineering)Engineering tolerance is the permissible limit or limits of variation in# a physical dimension,# a measured value or physical property of a material, manufactured object, system, or service,# other measured values ....
- ManufacturingManufacturingManufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
- Interference fitInterference fitAn interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening...
- Process capabilityProcess capabilityA process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
External links
- Engineer's Edge - IT Tolerance Grade Chart - All units shown in millimeters
- ISO Hole and Shaft tolerances/limits, Roymech, UK.
- ISO Hole and Shaft Tolerances iPhone App, Trelleborg Sealing Solutions Germany.