The ISO 286 system of limits and fits is the international standard for specifying dimensional tolerances in engineering. This calculator helps you understand how hole and shaft tolerances combine to create different types of fits: clearance, transition, and interference.
What Are Limits and Fits?
When a shaft is inserted into a hole, the relationship between their sizes determines the fit. A clearance fit always has a gap between the parts, an interference fit requires force to assemble (press fit), and a transition fit may result in either slight clearance or slight interference depending on the actual manufactured sizes.
How the ISO 286 System Works
Step 1 — Basic size: The nominal diameter common to both hole and shaft (e.g., 50 mm).
Step 2 — Tolerance grade (IT): IT grades (IT5–IT16) define the magnitude of the tolerance band. Lower grades mean tighter tolerances.
Step 3 — Fundamental deviation: A letter code (A–Z for holes, a–z for shafts) positions the tolerance band relative to the basic size. H = hole with zero lower deviation; h = shaft with zero upper deviation.
Step 4 — Limits: Max limit = Basic size + upper deviation; Min limit = Basic size + lower deviation.
Common Fits (Hole Basis System)
H11/c11 — Loose running fit: large clearance for contaminated or hot environments
H9/d9 — Free running fit: good for bearings, high-speed rotation
H8/f7 — Close running fit: moderate speed, accurate location
H7/g6 — Sliding fit: precise sliding motion, minimal play
H7/h6 — Locational clearance: easy assembly with minimal clearance
H7/k6 — Locational transition: snug fit, light press or tap to assemble
H7/n6 — Locational transition/interference: tighter transition fit
H7/s6 — Drive fit: medium press, permanent assembly
Step-by-Step Example: Ø50 H7/g6
Basic size = 50 mm → Size range 30–50 mm. IT7 = 25 µm, IT6 = 16 µm. Hole H7: EI = 0, ES = +25 µm → limits 50.000 to 50.025 mm. Shaft g6: es = −9 µm, ei = −25 µm → limits 49.975 to 49.991 mm. Min clearance = 0.009 mm, max clearance = 0.050 mm → Clearance fit.
Who Uses This Tool?
This calculator is ideal for mechanical engineering students, toolroom apprentices, design engineers, and anyone studying metrology, manufacturing processes, or machine design. Practice mode and quiz mode help prepare for exams and competency assessments.
