(Medium) is the most commonly used class in general mechanical engineering, offering a practical balance between manufacturing cost and precision for typical machined parts.

For radii and chamfer heights, the tolerance class applies but with reduced absolute values (see ISO 2768-1, Table 3). Typically, for class:

Historically, engineers had to annotate every single dimension on a drawing with a specific tolerance (e.g., $25.00 \pm 0.15$). This practice led to cluttered drawings and increased inspection costs. To mitigate this, the International Organization for Standardization (ISO) developed , a standard that defines general tolerances . These are tolerances applicable to dimensions that do not have an explicit tolerance indication.