The ISO 20457 standard (which succeeded DIN 16742) provides a standardized framework for tolerances and acceptance conditions for plastic molded parts. It defines tolerance groups (TG) ranging from TG1 to TG9, where lower numbers indicate higher precision. For many standard industrial thermoplastics, TG6 is the commonly used baseline for general tolerances. Key Tolerance Tables and Documents
While the full PDF requires purchase, several engineering portals (including ResearchGate, Academia.edu, and injection moulding forums) offer summary tables. These are useful for initial design but should never replace the official document for production contracts. A quick Google search for “iso 20457 tolerance table pdf free” may lead to draft versions or manufacturer-specific adaptations – verify the revision date (2020) and table numbers before use.
Before diving into the table itself, it is essential to understand the scope of the standard. ISO 20457:2018 is titled "Geometrical product specifications (GPS) — Classification of tolerances for dimensional and geometrical characteristics."
For general thermoplastics, the standard typically defaults to Tolerance Group 6 (TG6) unless otherwise specified.
Keep a legitimate copy of ISO 20457:2018 on your digital shelf, and you will never again guess whether a "±0.5mm" is appropriate for a 2-meter-long part.