Understanding ISO 2768-MH Tolerance Chart: A Comprehensive Guide
In the world of engineering and manufacturing, tolerances play a crucial role in ensuring that parts and components fit together seamlessly. One of the most widely used tolerance standards is ISO 2768, which provides a set of general tolerances for linear and angular dimensions. In this blog post, we'll dive into the specifics of the ISO 2768-MH tolerance chart, exploring its significance, application, and interpretation.
What is ISO 2768?
ISO 2768 is an international standard that defines general tolerances for linear and angular dimensions. The standard provides a set of tolerances that can be applied to various features, such as lengths, widths, heights, and angles. The goal of ISO 2768 is to ensure that parts and components can be manufactured and assembled with a reasonable degree of accuracy, while also allowing for some degree of variation.
Understanding the ISO 2768-MH Tolerance Chart
The ISO 2768-MH tolerance chart is a specific part of the ISO 2768 standard, which defines the tolerances for medium (M) and high (H) accuracy classes. The chart provides a set of tolerance values for different feature types, including:
The ISO 2768-MH tolerance chart consists of several columns, which represent the following:
Interpreting the ISO 2768-MH Tolerance Chart
To interpret the ISO 2768-MH tolerance chart, follow these steps: iso 2768-mh tolerance chart
For example, suppose we have a linear dimension with a nominal size of 100 mm. We want to apply a tolerance class M. According to the ISO 2768-MH tolerance chart, the tolerance value for a linear dimension with a nominal size between 80 mm and 120 mm is ±0.5 mm.
Significance of ISO 2768-MH Tolerance Chart
The ISO 2768-MH tolerance chart is significant in various industries, including:
Best Practices for Using the ISO 2768-MH Tolerance Chart
To get the most out of the ISO 2768-MH tolerance chart, follow these best practices:
Conclusion
The ISO 2768-MH tolerance chart is a valuable resource for engineers and manufacturers, providing a set of general tolerances for linear and angular dimensions. By understanding and applying the tolerances outlined in this chart, designers and manufacturers can ensure that their parts and components fit together seamlessly, while also minimizing costs and maximizing efficiency. Whether you're working in aerospace, automotive, or medical devices, the ISO 2768-MH tolerance chart is an essential tool to have in your toolkit.
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ISO 2768-mH designation is a widely used international standard for general tolerances in manufacturing, typically applied when specific tolerance values are not indicated on a drawing. It combines two parts: for medium dimensional accuracy (Part 1) and for high geometrical precision (Part 2). Linear Dimensions (m - Medium)
These tolerances apply to measurements like lengths, widths, diameters, and step distances. Nominal Dimension Range (mm) Tolerance (± mm) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Over 400 to 1,000 Over 1,000 to 2,000 Over 2,000 to 4,000 Xometry Standard Tolerances Geometrical Tolerances (H - High Precision)
The "H" class defines strict limits for form and position, such as how straight or perpendicular a feature must be. Straightness and Flatness Range of Nominal Length (mm) Tolerance (mm) Over 10 to 30 Over 30 to 100 Over 100 to 300 Over 300 to 1,000 Over 1,000 to 3,000
What is ISO 2768? | CNC Machining Tolerance Standards - Fictiv
To appreciate the 'm' and 'H', compare them to other classes.
| Class | Linear (6-30mm) | Geometric (Flatness per 100mm) | Typical Application | | :--- | :--- | :--- | :--- | | f (Fine) | ±0.05mm | 0.1mm | Precision instruments, aerospace backups | | m (Medium) | ±0.2mm | 0.2mm | General machining, welding fixtures | | c (Coarse) | ±0.5mm | 0.4mm | Sand castings, agricultural equipment | | v (Very Coarse) | ±1.0mm | 0.8mm | Rough fabrications, concrete molds | Linear dimensions (e
Why 'mH' is the default: 'f' is too expensive for base material. 'c' is too loose for mating holes. 'mH' balances cost and functionality for 80% of mechanical parts.
| Nominal Hole Size (mm) | Tolerance Grade (implied) | Tolerance (± or +/–) | |------------------------|---------------------------|----------------------| | ≤3 | IT13 | +0.14 / 0 | | >3–6 | IT13 | +0.18 / 0 | | >6–10 | IT13 | +0.22 / 0 | | >10–18 | IT13 | +0.27 / 0 | | >18–30 | IT13 | +0.33 / 0 | | >30–50 | IT13 | +0.39 / 0 | | >50–80 | IT13 | +0.46 / 0 | | >80–120 | IT13 | +0.54 / 0 | | >120–180 | IT13 | +0.63 / 0 | | >180–250 | IT13 | +0.72 / 0 | | >250–315 | IT13 | +0.81 / 0 |
✅ Example: A 20 mm diameter hole with no tolerance is allowed to be 20.00 mm to 20.33 mm. It can never be 19.98 mm.
⚠️ Important: H means only positive deviation (hole gets larger). This ensures assembly with shafts, pins, or bolts.
ISO 2768 is a standard providing general tolerances for linear and angular dimensions on technical drawings when no specific tolerance is indicated. This paper explains the scope and purpose of ISO 2768, details the tolerance classes (f, m, c, v), focuses on the “m” (medium) grade for machining (ISO 2768‑m), discusses the interpretation and application of ISO 2768‑m for linear, angular, and geometric features, shows worked examples and charts, comments on limitations and best practices, and compares ISO 2768 with other tolerance systems. Practical recommendations and a sample tolerance chart for ISO 2768‑m are included.
You might ask: Why not just tolerance every single hole and edge?
The answer is cost. Tight tolerances require grinding, lapping, and CMM inspection. If a 100mm long cosmetic cover plate is dimensioned at 100mm ±0.01mm because the drafter forgot to set defaults, the part will cost 500% more than necessary.
ISO 2768-mH provides a safety net:
The most critical part of this article is the actual chart. For general tolerances per ISO 2768-1, class Medium (m) , the tolerances are defined by nominal dimension ranges. Note that these are symmetrical tolerances (±) unless otherwise stated.
❌ Applying mH to shafts – H is for holes only. For shafts, use “mK” or specify individually.
❌ Assuming bilateral tolerances for holes – H holes are unilateral (+/0).
❌ Using mH for welded or cast parts – ISO 2768 is for metal removal (machining), not raw castings.
❌ Forgetting angular tolerances – 1 degree is large. If you need 0.5°, specify it.