ISO 286 Fits & Tolerances.
Hole-basis or shaft-basis fits, all classes from a1 to zc11. Get upper/lower deviations, clearance/interference, and fit type instantly.
Hole — H7
Shaft — g6
Common fits — when to use which
| Fit | Type | Use case |
|---|---|---|
| H7/h6 | Locational clearance | Locating accurate parts. Easy assembly with no measurable play. |
| H7/g6 | Sliding fit | Sliding shafts, parts that move without rotation (gears on splines). |
| H8/f7 | Running fit | Rotating shafts, journal bearings at moderate speed. |
| H9/d10 | Loose running | High-speed shafts, large temperature variation, dirty environment. |
| H11/c11 | Very loose | Pivoted joints, agricultural machinery, rough commercial work. |
| H7/k6 | Transition | Hand assembly with mallet. Bushings, gears requiring positional accuracy. |
| H7/n6 | Tight transition | Press-fit assembly with arbor press, parts that must not move under load. |
| H7/p6 | Light press fit | Permanent assembly, light press. Stable for moderate loads. |
| H7/s6 | Medium press fit | Heavy press, shrink-fit. Cast iron hubs on steel shafts. |
| H7/u6 | Heavy press fit | Permanent assembly. Bushings in housings, race fits in heavy industry. |
What are ISO 286 Fits?
ISO 286 is the international standard for limits and fits on cylindrical features (holes and shafts). It defines a system of tolerance grades (IT01 to IT18) and fundamental deviations (letters A-Z for holes, a-z for shafts) that combine to give standard fit classes.
Three Types of Fit
- Clearance Fit — Hole always larger than shaft. Free assembly. Examples: H7/g6, H7/h6.
- Transition Fit — Sometimes clearance, sometimes interference depending on actual sizes. Examples: H7/k6, H7/n6.
- Interference Fit — Shaft always larger than hole. Press-fit or shrink-fit assembly. Examples: H7/p6, H7/u6.
How ISO 286 Notation Works
Notation like ⌀30 H7/g6 means:
- ⌀30 — basic size (nominal)
- H7 — hole tolerance: H = fundamental deviation 0 (lower limit at nominal), 7 = grade IT7
- g6 — shaft tolerance: g = small clearance below nominal, 6 = grade IT6
For ⌀30, IT6 = 13 µm and IT7 = 21 µm. Hole is 30.000 to 30.021. Shaft is 29.980 to 29.993. Clearance ranges from 0.007 to 0.041 mm.
Common Fit Classes Worked Examples
H7/g6 (close running fit) — for journal bearings with oil film. Ø30 → clearance 0.007 to 0.041 mm.
H7/h6 (close clearance fit) — sliding fit, hand-assembled. Ø30 → clearance 0.000 to 0.034 mm.
H7/k6 (transition fit) — light press, mallet-assembled. Ø30 → -0.002 to +0.025 mm (sometimes interferes).
H7/p6 (light interference) — press-fit for small components. Ø30 → -0.022 to -0.001 mm (always interferes).
H7/u6 (heavy interference) — shrink-fit for high-torque hubs. Ø30 → -0.061 to -0.027 mm.
Choosing the Right Fit
- Free assembly + relative motion → H8/d9, H7/g6
- Sliding fit, no rotation → H7/h6
- Locating fit, removable → H7/n6, H7/k6
- Press-fit, permanent → H7/p6, H7/r6
- Heavy interference → H7/s6, H7/u6 (requires heating to assemble)
Common Mistakes
- Using same letter case for hole and shaft — H is hole, h is shaft.
- Forgetting that grade applies to both — H7/h6 is not the same as H6/h7.
- Not accounting for surface roughness when fit is tight — peaks and valleys reduce effective interference.
Related Tools
For interference fit force calculation, use Press-Fit Calculator. For position-toleranced holes, see Position Tolerance. Stack-up multiple fits with Tolerance Stack-Up. Document the fit on FAI Form 3 in AS9102 Form 3 Builder.