Ondermaat

Ondermaat is a Dutch term used in measurement, manufacturing and quality control to describe a part or dimension that falls below the specified nominal size. The word combines onder- meaning under, and maat meaning measure or size. In technical contexts, parts are produced within a tolerance range around a nominal dimension. The term ondermaat refers to measurements that are lower than the lower limit of the tolerance band, i.e., undersized components. The opposite, overmaat, refers to parts larger than the upper tolerance limit. A part that lies within the tolerance is called normale maat or nominal size.

Contexts: In mechanical engineering and metalworking, ondermaat components may still be acceptable if the design allows for it or they may require rework (machining, grinding) to bring them within specification. In quality control, records of ondermaat instances help identify tool wear, calibration drift, or process instability. In construction or woodworking, ondermaat can appear in joint fits or in lumber that is planed down below nominal dimensions, often corrected by shims or re-cutting.

Examples: A shaft specified as 20.00 mm with tolerance -0.05 mm might be rejected if it measures below 19.95 mm, i.e., undermaat. A wooden plank measured at 95.8 mm when the nominal dimension is 96 mm could be described as undermaat.

See also: overmaat, nominal size, tolerance, fit.

Note: The term is primarily used in Dutch-language technical literature and industry documentation; equivalents exist in other languages (e.g., Untermaß in German, under-size in English).

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