According to ISO 20457/DIN 16742, the realization of the required level of accuracy in the production of moulded parts requires an assignment to the tolerance series:

Series 1 (standard production): Production with general tolerances may be possible. Dimensional requirements are not a particular focus of quality. 

Series 2 (precise production): Production and quality assurance are oriented towards higher dimensional accuracy requirements. 

Series 3 (precision production): Complete alignment of production and quality assurance to the very high dimensional accuracy requirements

Series 4 (special precision production): Same as series 3, but with intensified process monitoring.

Tolerance series 3 and 4 are always subject to agreement


Only absolutely necessary small functional tolerances justify the production costs of series 3 and 4, which must be compensated for with a significant surcharge. Therefore, it must first be clarified between the customer and the manufacturer whether the tolerance requirements can be met. Self-deceptions are bad advisors for all cooperation partners. The following conditions should be checked with appropriate expertise:

  • Dimensionally accurate design and dimensioning of the moulded part.
  • Functional safety of tools that are sufficiently rigid and thermally and rheologically balanced.
  • Operation of necessary machines and systems by sufficiently qualified operating personnel including quality assurance.
  • Delivery conditions of the molding compounds with regard to dimensionally relevant properties, in particular fluctuations in shrinkage.

To support the assignment of the tolerance series, selection criteria for thermoplastic injection moulding are listed in Appendix D of DIN 16742 as examples. These selection criteria are taken into account internally by an extended selection algorithm.