Convert a precision class and nominal size into the allowed bore or OD range, and calculate ISO 286 IT-grade tolerances for the size step you are working in.
The first block applies ISO 492 deviations to a nominal bore or outside diameter: enter the nominal size, choose the precision class, and the tool returns the lower limit and the allowed bore range. This is the number to check against an incoming goods measurement.
The second block computes ISO 286 IT grades from the standard tolerance unit i = 0,45 · ∛D + 0,001 · D (for sizes up to 500 mm), where D is the geometric mean of the size step. IT5 is 7i, IT6 is 10i, IT7 is 16i, IT8 is 25i, IT9 is 40i, IT10 is 64i and IT11 is 100i. The result is the width of the tolerance zone, not its position - a shaft dimension must still carry its letter, because h places the zone below nominal, k and m above it.
A precision class describes the bearing; an IT grade describes the shaft or housing it sits in. Raising the bearing class tightens the bearing and changes the runout, but it does not make the seat tighter. If a shaft is too tight for the bearing's bore, the problem is the shaft tolerance, not the bearing class. See tolerances and clearance and fit recommendations.
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