ISO Tolerance Bands

The tolerance of size is normally defined as the difference between the upper and lower dimensions.

The need for tolerances to be identified on drawings is vital to allow assembly of parts in the desired way and interchangeability of parts as required in modern manufacturing methods.

ISO 286 implements 20 grades of accuracy to satisfy the requirements of different industries.

IT01,  IT0,   IT1,  IT2,   IT3,  IT4,  IT5,  IT6.. Production of gauges and instruments.

IT5,  IT6,  IT7,  IT8,  IT9,  IT10,  IT11,  IT12.. Precision and general Industry.

IT11,  IT14,   IT15,  IT16.. Semi finished products

IT16,  IT17,  IT18.. Structural Engineering

Examples in using above tables..

Note: The tolerance band T is an absolute length value it does not have a negative value.

Hole Dia 110mm H11,...

Nearest zero ( El )= 110mm + 0mm = 110,000mm ..

Furthest from zero ( ES )= 110mm + (0+ T=0,220)=110,220mm

Resulting limits 110,000/110,220

Shaft 110mm e9...

Nearest zero ( es ) = 110mm - 0,072=109,928mm...

Furthest from zero ( ei ) = 110mm - (0,072 + T=0,087) = 109,841mm

Resulting limits 109,928/109,841

Note for the tolerance bands which can be either side of zero, (J,K,N,j )

The diagrams provided with the table clearly show calculation needed.e.g. consider Hole 300K7.

T= 52 micrometres (0,052mm). Limit nearest zero ( K ) ES = 16 micrometres = (0,016mm)

Limit furthest from zero ( K ) El = (0,016- 0,052)= -0,036

Limits therefore (300 -0,036) = 299,964..and ...300+0,016= 300,016 limits 299,964/300,016 tolerance band in micrometres = (m-6) based on ISO 286  IT Grades 1 to 14  

ISO Tolerance Band "T " 0 to 315mm

ISO Tolerance Band "T " 315 to 3150mm