Technical Paper: Understanding Tolerance Tables in ISO 20457
Subject: Dimensional Tolerances for Thermoplastics Pipes and Fittings Standard Reference: ISO 20457:2017 (Plastics pipes and fittings — Dimensions and tolerances)
It includes specifications for surface profiles, angular dimensions, and tool offsets (parting lines). OKW Gehäusesysteme Reference Documents & Tables
The ISO 20457 standard (formerly DIN 16742) defines the manufacturing tolerances and acceptance conditions for plastic molded parts. It is primarily used to align expectations between designers and manufacturers regarding dimensional accuracy in injection molding and other plastic processes. Key Tolerance Group: TG6
: Materials are categorized (typically Categories 1–4) based on their shrinkage properties. Precision Classes Class A (High Precision)
| Nominal Size Range (mm) | Fine (f) Tolerance (± mm) | Medium (m) Tolerance (± mm) | Coarse (c) Tolerance (± mm) | | :--- | :--- | :--- | :--- | | 0.5 up to 3 | 0.05 | 0.1 | 0.2 | | 3 up to 6 | 0.1 | 0.2 | 0.5 | | 6 up to 30 | 0.2 | 0.5 | 1.0 | | 30 up to 120 | 0.3 | 0.8 | 1.5 | | 120 up to 400 | 0.5 | 1.2 | 2.5 | | 400 up to 1000 | 0.8 | 2.0 | 4.0 | | 1000 up to 2000 | 1.2 | 3.0 | 6.0 | | 2000 up to 4000 | 2.0 | 5.0 | 10.0 |
When to consult the PDF/standard directly
- Grade 1–2: For precision fits (gears, bearing housings, medical devices)
- Grade 3: General-purpose engineering parts
- Grade 4–5: Non-critical housings, cosmetic covers, large parts