| Tolerance Grade | Primary Application | Relative Precision | Material Examples | Key Design Guidance | | :--- | :--- | :--- | :--- | :--- | | | Packaging parts, high-volume consumer goods | Coarse; lowest cost | PP (polypropylene), LDPE | Tolerances wide enough to absorb high shrinkage with good molding consistency | | TG4 | Precision parts (gears, bearings, complex assemblies) | Fine; premium cost | POM (acetal), PC (polycarbonate), filled nylons | Often reserved for critical CTQ dimensions; requires tight process control and specific material | | Tg5 (Focus) | Housings, general mechanical parts, standard enclosures | Medium; optimized cost-performance | ABS, unfilled PC/ABS, general-purpose thermoplastics | Ideal default for "W" dimensions; use ±0.3 mm (up to 120mm) as typical vision for costing and assembly | | TG6 | Baseline commercial quality for large parts | Medium-coarse; cost optimized for size | ABS, PP, commodity resins | When part envelope exceeds 300 mm and tight flatness is not needed; relax surface profile to avoid core-out penalties | | TG7 | Very large structures, rotational molding | Very coarse; minimum manufacturing cost | PE (polyethylene), soft elastomers | Only use on non-mated surfaces, total envelope > 1m, or when mold is still under development |
The typical tolerance values associated with Tg5, which vary based on the nominal size of the dimension in question, are as follows:
To understand TG5, one must first understand the structure of ISO 20457. The document is divided into several clauses (TG stands for "Technical Group" or clause grouping in some internal drafting contexts, though in common industrial parlance, TG5 refers to focusing on Test methods for specific properties ).
Excellent dimensional stability and impact resistance. Iso 20457 Tg5
| Nominal Dimension (mm) | General Tolerance (±mm) | | :--- | :--- | | up to 3 | ±0.10 | | 3 to 6 | ±0.15 | | 6 to 30 | ±0.20 | | 30 to 120 | ±0.30 | | 120 to 400 | ±0.45 | | 400 to 1000 | ±0.80 | | 1000 to 2000 | ±1.20 |
: Ultra-precision / Fine tolerances (typically reserved for medical, aerospace, and high-end optical systems).
: TG5 typically represents a "standard" or "simple" production level for certain materials like ABS . | Tolerance Grade | Primary Application | Relative
Choosing indicates that your component can handle moderate dimensional variations without failing its real-world application. It accommodates the natural physical dynamics of unreinforced or minimally filled engineering resins during the cooling cycle. 1. Dimensional, Flatness, and Straightness Metrics
The standard uses a hierarchy of Tolerance Groups (TGs) to categorize the level of manufacturing effort required:
ISO 20457 (which replaced DIN 16742 ) provides a framework for agreeing on dimensional, shape, and position deviations in plastics, which behave differently than metals due to shrinkage and polymer properties. | Nominal Dimension (mm) | General Tolerance (±mm)
Simply stating "ISO 20457 TG5" on a drawing is often considered insufficient for a binding contract. According to the ISO 20457 Guide , a complete enforceable specification should include: TG5.
: Selecting TG5 implies a commitment to higher manufacturing costs compared to standard grades like TG6 or TG7. Tighter tolerances require more expensive tooling, tighter process controls, and more frequent quality assurance checks. Material Influence
Designing for TG5 does not require the same exorbitant tooling costs as TG1 or TG2. The mold can be cut with standard CNC machining methods rather than requiring exotic micro-machining.
Housings for medical instruments and syringes.