This page explains where the numbers in the tolerance calculator and the individual class pages come from, what has been verified, and which combinations we deliberately leave out. For engineering purposes, always rely on the drawing and the current official standard.
| Standard | ISO 286-1 (tolerance classes and fundamental deviations) |
|---|---|
| Verified on | 2026-08-26 |
| Result | 6,674 valid cells compared one by one: 6,674 correct, 0 wrong |
| Coverage | Shafts a b c d e f g h j js k m n p r s t u v x y z, holes the same letters in uppercase; grades IT1–IT13; nominal sizes 0–500 mm |
| Not included | cd / ef / fg / za / zb / zc (watchmaking and extreme interference), sizes above 500 mm, grades above IT13 — always reported as "not found"; values are never extrapolated or guessed |
"Independent" means the three do not share one original table. Whenever a cell disagrees among the three we trace it back; there is no majority vote.
The whole grid of 22,568 cells was taken (letter × case × IT1–13 × 25 size ranges). It has three known defects, each handled individually rather than adopted as is:
Computed from the fundamental-deviation formulas and the IT table, then compared cell by cell with source 1. All differences are within ±4 µm (caused by ISO rounding the a/b/c/d/e/f rows to convenient numbers), and not a single cell shows a whole-column shift — the most common transcription error and the hardest to spot by eye; we confirmed it did not occur.
The anchor is a customer's actual engineering drawing: Ø3 m6 = +0.008/+0.002. 32 cells of IT5–IT8 in the first eight size ranges and 28 cells of the f / g / h / m fundamental deviations were compared with the first two sources: all agree.
The verification scripts are kept in-house. Changing any number requires re-running the whole procedure; nothing is edited from memory. The tolerance charts on this site, the calculator, the individual class pages and our internal tools all use the same table, so the tool and the pages can never disagree.
If you find a cell that does not match, please e-mail sfp@sfp-tw.com with the size and class; we will trace it and update this page.
Values follow ISO 286-1; the table was cross-checked cell by cell against three independent sources on 2026-08-26 (6,674 cells agree, 0 errors). Coverage: shafts a–z and the corresponding uppercase holes, IT1–IT13, nominal sizes 0–500 mm. cd/ef/fg/za/zb/zc, sizes above 500 mm and grades above IT13 are not included: the tool reports "not found" and never extrapolates. Data sources and verification →
Values follow ISO 286-1; the table was cross-checked cell by cell against three independent sources on 2026-08-26 (6,674 cells agree, 0 errors). Coverage: shafts a–z and the corresponding uppercase holes, IT1–IT13, nominal sizes 0–500 mm. cd/ef/fg/za/zb/zc, sizes above 500 mm and grades above IT13 are not included: the tool reports "not found" and never extrapolates. Data sources and verification →