What Are Engineering Tolerances

An engineering tolerance is the allowable amount of variation in a specific measurement from its base value, also known as the nominal value. Tolerances can be specified for any measurement (temperature, weight, volume, current, voltage, etc.) but tolerances specified in mechanical engineering generally apply to linear, angular and other physical dimensions and are found on the technical drawing.

Since no manufacturing process is perfect, every part that has ever been manufactured has had some amount of variation in its dimensions or geometry, even if it is slight. This will always be the case – a rubber D-section with a specified wall thickness of 10 mm will never be exactly that but may end up 10.5 mm when extruded.

Different industries work to different engineering tolerances. The 0.5 mm variation in the rubber D-section above might not seem significant, and it’s not in the rubber extrusion industry, but a 0.5 mm variation in the aerospace industry is quite large. Therefore, it is important to understand the relevant tolerances of your industry and know how to apply them correctly – read our other articles to discover ways of doing this.

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