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Suppose the fit for a rod and a hole in a gear is supposed to be free running and the fit is 3mm H9/d9. For the specification of the hole for the manufacturing of the gear, is "3mm H9" already adequate since d9 only refers to the shaft tolerance which may not be pertinent to the manufacturing of the gear? Sometimes I see the fit specified on drawing sheets for some reasons, e.g., "10mm H9/d9".

If my understanding is correct, 3mm H9 essentially means 3mm - 3.025mm and 3mm d9 means min. 2.955mm - 2.98mm. So the clearance ranges from 0.02mm to 0.07mm - am I right?

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Your clearance range is the minimum hole diameter minus max shaft diameter to max hole diameter minus minimum shaft diameter.

Answer: Yes. Your math seems correct.

This is a useful tool: http://www.amesweb.info/FitTolerance/FitTolerance.aspx

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