As the nominal size of the part increases, the allowable tolerance window expands to accommodate the higher volume of material shrinkage. Simplified Preview of an ISO 20457 Tolerance Table
Specifying only “ISO 20457” on a drawing is insufficient. The standard defines multiple tolerance grades, and without specifying TG4, TG5, TG6, etc., your manufacturing partner has no way of knowing which tolerance band applies. iso 20457 tolerance table pdf
For engineers, quality managers, and procurement professionals working with injection-molded plastic parts, precision is everything. However, the properties of plastics—from material shrinkage to thermal expansion—make them fundamentally different from machined metals. Applying metal tolerances to plastic parts inevitably leads to costly rework, rejected shipments, and strained supplier relationships. This is where comes into play. As the nominal size of the part increases,