Before examining the tables, it is necessary to understand why ISO 20457 exists. Older national standards (such as DIN 7168 or ISO 2768) served the same purpose: to define default tolerances for dimensions and geometry that are not individually specified on a drawing. ISO 20457 supersedes and harmonizes these earlier standards into a single GPS framework. The standard allows a designer to state in a title block or note: “General tolerances according to ISO 20457 – medium class.” This single line replaces dozens of individual tolerance notes, reducing drawing clutter and ensuring that simple features—like a chamfer, a non-critical length, or a flat surface—receive a reasonable, shop-floor-friendly tolerance without explicit callouts.
The bridges this gap. It establishes standard tolerance blocks and surface profile criteria within a defined Geometrical Product Specification (GPS) datum framework. It helps stakeholders explicitly delineate between "general tolerances" (applied broadly to non-functional attributes) and "direct tolerances" (assigned to hyper-critical, tight-fit assembly dimensions). TOLERANCES
Note: This table is a representative summary. The official ISO 20457 PDF contains exact values and footnotes regarding chamfers, radii, and external/internal dimensions. iso 20457 tolerance table pdf
Choosing the right tolerance grade is a balance between functional requirements and manufacturing cost.
Automotive connector housings, high-end consumer electronics. Standard Precision Baseline industrial applications, structural brackets. TG6 Coarse Precision Before examining the tables, it is necessary to
ISO 20457 is an indispensable tool for anyone involved in the design, molding, or sourcing of plastic parts. By using its tolerance tables and systematic approach, you can avoid costly rework, ensure proper assembly, and achieve reliable quality. The shift from experience-based guesswork to a structured system like ISO 20457 is a foundational step in professionalizing plastic parts engineering.
You cannot apply a blanket tolerance to plastic parts. ISO 20457 calculates tolerances by evaluating four distinct pillars of the molding process: 1. Tooling Accuracy The standard allows a designer to state in
Searching for an typically means you want immediate access to these numerical values without purchasing the full 30-page document. However, understanding the logic behind the table is essential before applying any numbers.
Whether using injection molding, compression molding, or rotational molding, achieving high precision in plastics requires accounting for unique polymer characteristics like shrinkage, moisture absorption, and thermal expansion. 🛠️ The Purpose of ISO 20457
A company is designing a mounting bracket for an electric motor. The bracket is a sheet metal part (2mm thick, 200mm long). The motor has a shaft that aligns to a hole.
PT2 tolerance: ±0.30 mm