Istmaß

Istmaß is a term used in manufacturing and metrology to denote the actual size of a part or feature as measured during inspection. It refers to any linear dimension, such as length, width, diameter, or depth, and is determined with measuring instruments such as calipers, micrometers, height gauges, bore gauges, or coordinate measuring machines.

Istmaß is compared with the Sollmaß, the nominal size specified by the design. The tolerance defines the acceptable deviation around the Sollmaß, typically described by lower and upper specification limits. The deviation, often written as Δ = Istmaß − Sollmaß, indicates whether a part complies with the specification. Parts with Istmaßen inside the tolerance are accepted; those outside may be rejected or require rework.

In practice, a measurement plan governs how Istmaß is determined, including instrument calibration and measurement uncertainty. Measurements can be taken once or repeatedly, and statistical approaches may be used to summarize results (for example, mean, range, or distribution across a batch). The concept of Istmaß is closely tied to tolerancing standards, such as ISO 286, and to broader quality management practices.

Istmaß data support quality control and process capability assessment. They are used to monitor production, drive decisions about scrap or rework, and track trends that may indicate tool wear or process drift. In many industries—mechanical engineering, automotive, and aerospace, among others—Istmaß measurements help ensure interchangeability and reliable function of components across assemblies.

Example: a nominal size Sollmaß of 50.00 mm with a tolerance of ±0.05 mm yields an acceptable Istmaß range of 49.95–50.05 mm. An Istmaß of 50.03 mm is within tolerance; 50.07 mm is not.