Limit-and-fit engine for design and quality engineers: ISO 286-1 tolerance grades from the standard tolerance factor i = 0.45·∛D + 0.001·D, fundamental deviations for holes (G, H, JS, K, M, N, P) and shafts (d, e, f, g, h, js, k, m, n, p) including the Δ-rule for K/M/N/P holes, limit sizes, maximum/minimum clearance or interference, automatic fit classification (clearance / transition / interference), a tolerance-zone diagram and clearance-vs-diameter sensitivity. Every input with selectable universal units, every report with the full audit trail.
SectorCalc SC-027 computes ISO 286-1 limits and fits from first principles: the standard tolerance factor i = 0.45·∛D + 0.001·D evaluated at the size-step geometric mean, grade multipliers (IT6 = 10i … IT11 = 100i), and the published fundamental-deviation formulas for the most-used hole and shaft classes. The engine returns limit deviations, limit sizes, maximum and minimum clearance or interference, and the fit classification, with a tolerance-zone diagram. Formula results reproduce the printed ISO tables within about ±2 µm (standard rounding rules) — for inspection disputes, the printed standard governs.
Tolerance grows with the cube root of size, not linearly — a 200 mm bore cannot hold the same absolute tolerance as a 20 mm bore on the same machine. Grades are geometric: each grade is roughly 1.6× the previous, so jumping one grade finer costs disproportionate process capability.
The letter positions the zone, the grade sets its width. Hole classes mirror the shaft of the same letter: G hole = −g shaft, H hole = zero lower deviation. This symmetry is what makes hole-basis and shaft-basis systems interchangeable.
For K, M, N (grades 3–8) and P–ZC (grades 3–7) the hole is not a pure mirror of the shaft — the Δ correction keeps transition and interference fits equivalent between hole-basis and shaft-basis assemblies. The engine applies it automatically; M7 holes, for example, come out symmetric about zero for most sizes.
Classification uses the worst-case corners, never the means. A transition fit (e.g. H7/k6) can assemble with slight clearance or slight interference depending on where the parts land in their zones — that ambiguity is exactly what the designer is buying for location without a press.
Rules of thumb validated by the database: H7/g6 for precision sliding parts that must be hand-assembled; H7/f7 for lubricated running fits; H7/js6 or H7/k6 for located parts (couplings, gears on shafts with keys); H7/n6 and H7/p6 for semi-permanent and light press assembly; beyond p6 (r, s, u classes) the assembly force and hoop stress must be calculated explicitly — this engine stops at p and says so.
The printed standard applies rounding rules to the formula values. This engine evaluates the ISO 286-1 formulas directly and rounds to 1 µm; differences of ±2 µm against printed tables are expected and stated in the assumptions. For disputes, the printed standard governs.
No — the fit tells you the interference band; converting interference into assembly force and hub stress needs a thick-cylinder calculation (Lamé) with surface roughness flattening. That is deliberately out of scope above p6.
Hole basis (H hole, letter-varied shaft) unless you have a reason: reamers and boring tools are fixed-size, shafts are cheap to grind to any diameter. Shaft basis makes sense on long shafts carrying several different components, or with cold-drawn bar stock (h9/h11).
Differential thermal expansion (aluminium housing, steel shaft) eats clearance at ~12–23 µm/m·K; plated or coated surfaces add 5–25 µm per side. Both must be added to the calculated band — the engine reports the drawing fit at 20 °C reference temperature.
