ISO Fits and Tolerances Calculator
Compute ISO 286 hole and shaft limits at any nominal size, with max and min clearance and whether the fit is clearance, transition or interference.
ISO 286 is tabulated to 500 mm. The hole and the shaft share this nominal size.
Pick a named fit, or set the hole and shaft yourself below.
H7/h6 is a clearance fit: locational clearance
The parts always have space between them. They assemble without force at every point in both tolerance bands.
Limits
Resulting fit
When this fit is used
Assembles by hand, locates well. The default clearance fit.
An ISO 286 fit is two tolerance zones, one on the hole and one on the shaft, and what matters is how they overlap. This calculator gives the limits for both in micrometers and millimeters for any nominal size to 500 mm, the resulting maximum and minimum clearance, and whether that combination is a clearance, transition or interference fit.
How to read the result
Hole basis is the practical default. Holes are cut with standard reamers and boring cycles, so it is cheaper to hold the hole at H and move the shaft, which can be turned to any diameter, than the other way around. Every preset here is hole basis for that reason.
The letter sets where a tolerance zone sits relative to nominal, and the number sets how wide it is. H7/h6 and H7/p6 share the same hole and the same shaft width, and differ only in where the shaft zone sits: one assembles by hand, the other needs a press. Changing the letter changes the fit; changing the number changes the cost.
Read the minimum clearance row first. A transition fit has positive maximum clearance and negative minimum clearance, which means the assembly is sometimes slightly loose and sometimes slightly tight depending on where each part lands in its tolerance band. If your design cannot tolerate both outcomes, you need a clearance or an interference fit, not a transition.
Frequently asked questions
- What does H7/h6 mean?
- The hole is held to grade IT7 with its lower limit at nominal, and the shaft to grade IT6 with its upper limit at nominal. The parts therefore never interfere and never have more than the summed tolerances of clearance. It is the standard locational clearance fit: assembles by hand, locates accurately, no play beyond the tolerances.
- What is the difference between a clearance, transition and interference fit?
- A clearance fit always has space between the parts, so minimum clearance is zero or positive. An interference fit always has material overlap, so maximum clearance is zero or negative and the parts must be pressed or heated to assemble. A transition fit straddles zero and can come out either way within the tolerance bands.
- Which fit should I use for a bearing?
- Follow the bearing maker's recommendation rather than a general table, because it depends on which ring rotates relative to the load. As a starting point, a rotating inner ring on a shaft commonly uses k6 or n6, and a stationary outer ring in a housing commonly uses H7. Getting this backwards lets the ring creep and fret.
- How tight a tolerance can machining actually hold?
- IT7 is routine on CNC equipment and IT6 is achievable with care and in-process gauging. Below IT6 you are into grinding, honing or lapping, with temperature control and inspection cost that usually exceeds the machining. Specify the loosest grade that works, since each step tighter adds cost without adding function.
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