That stance paid off in unexpected ways. A hospital purchasing manager came by, impressed by their documentation and careful QA. Medical device components and precision instruments followed—products where a near-micrometer variance could mean the difference between success and failure. Contracts that required adherence to standards were awarded to shops that could prove they understood them. Ana's shop was one such place.
Imagine designing a gearbox. The gears inside require "Fine" tolerances, but the outer cast housing only needs "Coarse" tolerances. ISO 20457 provides a systematic way to assign these levels without over-specifying (which increases cost) or under-specifying (which causes assembly failure).
Note: The format +X / 0 indicates that the pipe can be larger than nominal by X mm, but cannot be smaller than the nominal size (ensuring it can seal).
Determine the shrinkage factor of your chosen resin (e.g., ABS, PC, PA66). iso 20457 tolerance table pdf
Plastics shrink as they cool. Amorphous materials (like Polycarbonate) shrink evenly, while semi-crystalline materials (like Polypropylene) or glass-filled polymers shrink unevenly (anisotropy). ISO 20457 classifies materials into specific groups based on their processing shrinkage variance. 2. Evaluation Level (Production Accuracy)
If you need to calculate a specific for a project, feel free to share your nominal dimensions , plastic material type , and whether the features are tool-dependent , and I can help you find the exact values. Share public link
| Nominal Size (mm) | Fine Tolerance (approx.) | Medium Tolerance (approx.) | Coarse Tolerance (approx.) | | :--- | :--- | :--- | :--- | | up to 10 mm | ±0.05 mm | ±0.10 mm | ±0.20 mm | | >10 mm up to 50 mm | ±0.10 mm | ±0.20 mm | ±0.30–0.40 mm | That stance paid off in unexpected ways
Licensed engineering document distributors (like IHS Markit or Techstreet) Conclusion
for a TG3 fit) while letting the rest of the body fall back to the general TG specification. Why You Need the Official PDF
): The variations caused by fluctuations in injection pressure, melt temperature, cooling time, and ambient factory humidity. The total permissible tolerance ( AGcap A sub cap G ) is calculated geometrically combining these factors: Contracts that required adherence to standards were awarded
When reading an ISO 20457 table, you must distinguish between two types of dimensions because they handle tolerances differently:
ISO 20457 is the direct international successor to the German national standard DIN 16901, and the two are closely related. However, there are key differences:
Angles are treated differently because the deviation is measured as a length over a given length (mm/m) or directly in degrees/minutes.
National standards bodies like (United States), DIN (Germany), or BSI (United Kingdom).
Because ISO standards are copyrighted intellectual property, the official, fully detailed must be purchased through authorized channels. Legitimate sources include: The official ISO Store (iso.org)