Interesting rule of thumb: moving from costs ~2–3x more; IT5 to IT4 costs another ~2–3x. That’s the “tolerance-price cliff.”
The ISO system uses a clever alphanumeric code to define tolerance. If you have ever seen a drawing with a notation like , g6 , or P6 , you are looking at ISO tolerance codes. iso tolerance standards
ISO standards classify fits into:
Over-specifying (e.g., using H7/s6 where H7/k6 works) increases cost non-linearly without functional benefit. ISO helps you choose the right tolerance, not the tightest. Interesting rule of thumb: moving from costs ~2–3x