H7/g6 fit
Also called: ISO fit · ISO 286 tolerance · H7
H7/g6 is an ISO fit between hole and shaft: letters set the tolerance position and numbers the grade, defining clearance or interference.
ISO fits (ISO 286) define how a shaft fits a hole. The letter sets the tolerance position relative to the nominal size (uppercase for holes, lowercase for shafts) and the number sets the precision grade (IT). H7 is the most common hole: it starts exactly at nominal size and has a grade 7 tolerance.
How it works
Pairing hole and shaft sets the behavior: H7/g6 gives a small clearance (sliding, great for guide pins and slow-turning shafts); H7/h6 is a close sliding fit; H7/k6 is a transition fit (light press); H7/p6 is an interference fit (pressed). For a ⌀20 H7 hole the range is 20.000 to 20.021 mm; a ⌀20 g6 shaft goes from 19.980 to 19.993 mm.
Practical example
A bronze bushing must stay locked in its housing and a shaft must rotate inside it. The housing gets ⌀30 H7 with the bushing at p6 (pressed), and the bushing bore ⌀16 H7 with the shaft at f7 (running clearance). The drawing makes clear to machining and inspection what is acceptable.
Common mistakes
- Calling H7 on holes that do not mate with anything, raising cost.
- Giving only letter and number without nominal size or the limits table on the drawing.
- Forgetting that coating or plating changes the final size.
FAQ
Why is the hole usually H?
Because standard tools (drills, reamers, gauges) are made for H holes. It is cheaper to adjust the shaft and keep the hole on the hole-basis system.
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Related service
Manufacturing documentation
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