ISO 286 Limits & Fits Calculator
H7/g6, H7/p6 and every common fit in between: enter a nominal diameter and a fit, get the exact hole and shaft limits, the clearance or interference range, and a drawn fit diagram. Then flip it — enter two measured parts and check whether they are actually in limits and what fit you really have. IT grades per the published ISO 286 table. No sign-up.
1 to 500 mm.
Holes: D–JS · shafts: d–p. (s/u press fits use sub-divided ranges — ask us or see the standard.)
Inspection mode: you have real parts and a drawing callout — are they in limits, and what condition will the pair actually give?
How ISO limits and fits work — H7/g6 in plain English
A fit callout like Ø25 H7/g6 is two tolerance zones. The capital letter is the hole, the lower-case letter the shaft; the letter sets where the zone sits relative to nominal, and the number (the IT grade) sets how wide it is. H means the hole starts exactly at nominal and goes up; g means the shaft sits a little below nominal. Put them together and every possible pair of in-tolerance parts has between 7 and 41 µm of clearance at Ø25 — a snug sliding fit, every time, with no fitting or selection.
Most engineering uses the hole-basis system — the hole is always H, and you choose the shaft letter to get the fit — because holes are made with fixed-size tools (drills, reamers) while shafts are easily turned or ground to any diameter. The classic set runs from loose running fits (H9/d9, H8/f7), through sliding and location (H7/g6, H7/h6), transition fits that may be tight or slightly loose (H7/k6, H7/n6), to the light press fit H7/p6 where the parts are always in interference and need force or temperature to assemble.
The part most people have to look up twice: a transition fit is a probability, not a guarantee. H7/k6 at Ø25 can be anywhere from 6 µm clearance to 15 µm interference depending on where each part lands in its zone. If your design genuinely needs guaranteed interference, that is p6 territory (and our press-fit calculator will tell you the force); if it needs guaranteed clearance, stay at g6 or looser. Using k6 and hoping is how location pins end up loose in service.
Standard tolerance grades matter for cost too: each IT step is roughly 1.6× the tolerance of the one below, and cost moves the other way. IT7/IT6 (the H7/g6 world) is normal precision machining and comfortably inside our ±0.010 mm standard; IT5 and below is where grinding, honing and temperature-controlled inspection enter the conversation. If a fit matters, tell us the function — not just the numbers — at quotation.
Limits and fits — FAQ
What does H7/g6 mean?
It is an ISO 286 fit callout. H7 is the hole tolerance zone (starts at nominal, width IT7 — +21/0 µm at Ø25); g6 is the shaft zone (slightly below nominal — −7/−20 µm at Ø25). Together they guarantee a small clearance: between 7 and 41 µm at Ø25. It is the classic precision sliding fit.
What is the difference between H7/h6, H7/k6 and H7/p6?
H7/h6 is a location clearance fit — from zero to small clearance. H7/k6 is a transition fit: depending on where each part falls in tolerance it can be slightly loose or slightly tight, so it locates well but is not guaranteed interference. H7/p6 is a true light press fit — always interference, needing force or thermal assembly.
What tolerance is H7?
H7 means the hole may be up to one IT7 grade above nominal and never below it. IT7 depends on size: 15 µm at 6–10 mm, 18 µm at 10–18, 21 µm at 18–30, 25 µm at 30–50, 30 µm at 50–80. So a Ø25 H7 hole is 25.000 to 25.021 mm.
Should I use hole-basis or shaft-basis fits?
Hole-basis (H holes, varied shafts) in almost all cases — holes are made by fixed-size tooling, shafts are easy to adjust. Shaft-basis (h shafts, varied holes) appears where one shaft carries several parts with different fits, e.g. a long drive shaft.
Can CNC machining hold H7 or g6?
Yes — IT6/IT7 fits are standard precision machining territory and within our ±0.010 mm standard tolerance. Grades IT5 and finer usually involve grinding or honing plus temperature-controlled inspection, which is a cost conversation worth having at quotation.
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