ISO Tolerance Table (H7 h7 Fits) - Machining Tolerance Chart & Clearance Fit Guide
⚠️ NOTICE: Metric (mm) Unit Standards Only This chart is strictly for Metric-based drawings (ISO, KS, JIS, DIN). For U.S. Customary (Inch) drawings, please refer to the ASME Class RC/FN charts, as the tolerance systems are not interchangeable.
ISO Fits & Tolerances Table (H7 / h7 Basis)
"According to ISO 286-2 (Geometrical product specifications - ISO code system for tolerances on linear sizes)"
Unit: μm (micrometer, 0.001mm)
.webp)
H7 (Uppercase): Hole-basis system. It defines internal features typically produced by drilling, boring, or end-milling. This standard generally applies a (+) tolerance to ensure adequate clearance for the shaft. (Lower Limit: 0 / Upper Limit: +)
h7 (Lowercase): Shaft-basis system. It refers to external features such as pins, rods, or precision shafts. A (-) tolerance is typically applied to ensure a smooth, precise fit into the corresponding hole. (Upper Limit: 0 / Lower Limit: -)
"Note: For 'Øn~n', please refer to the table to apply the tolerance for your specific size."
Refined Version
Why is H7/h7 the Standard? This combination provides a highly precise "Clearance Fit." It offers a smooth, tactile feel when assembled by hand—sliding in effortlessly with zero rattle or play. This is why it remains the gold standard for machining bearing seats and guide pin holes.
Pro Tip (From a Veteran MCT Machinist) "Never treat a dimension as 'just a number.' Even if a drawing simply states '10mm,' if that spot is for a bearing, you must aim for an H7 (+0.015) tolerance to avoid costly defects. In my experience, ignoring these specific fit requirements is a direct path to assembly failure."
"Some designers use labels like 'Press Fit' or 'Clearance Fit' instead of providing specific numerical tolerances. In these cases, a reliable rule of thumb for the hole-basis system is to aim for -0.01mm for Press and +0.01mm for Clearance. For exact specifications, always refer to the standard tolerance table."
"Working with Imperial (Inch) drawings? Stay tuned! I'll be diving into ANSI/ASME B4.1 tolerances in my next post."
[Disclaimer] This article is based on the author's experience and knowledge. AI assistance was used solely for translation and editorial refinement to enhance readability. The content has been personally reviewed and verified by the author and is provided for informational purposes only.
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