The ISO 20457 tolerance table, found within the standard’s PDF, is a cornerstone of modern geometric product specification. It translates the abstract concept of “general tolerance” into specific, actionable numbers for linear dimensions, angles, flatness, straightness, perpendicularity, and runout. By organizing these values into four clear classes (f, m, c, v), the standard balances manufacturing economy with functional assurance. For any design engineer or manufacturing professional, understanding how to read and apply the tables in ISO 20457 is not a niche skill—it is a fundamental practice that turns a drawing into a reliable, producible product.
ISO 20457 (and its German equivalent DIN 16742) is the international standard for dimensional and geometrical tolerances of plastic molded parts. It replaces older standards like DIN 16901 to provide a more consistent framework for injection molding and related processes. Key Tolerance Tables & TG Groups
The standard classifies tolerances into Tolerance Groups (TG), typically ranging from TG1 to TG9. TG6 is the most common baseline for commercial plastic parts. Nominal Dimension (mm) TG4 (Precision) TG6 (General) TG8 (Coarse)
Values are approximate based on standard industry applications of ISO 20457/DIN 16742. How to Choose a Tolerance Group
Choosing the right TG depends on the material's shrinkage behavior and the part's functional requirements.
Material Family: Amorphous resins (e.g., ABS, PC) have lower shrinkage and can often achieve TG4 or TG5. Semi-crystalline resins (e.g., PA66, POM) have higher shrinkage and usually require TG6 or higher.
Production Difficulty: Tighter groups (TG1–TG3) are rarely used as they significantly increase mold costs and scrap rates.
Baseline Standard: Most engineering components default to TG6 unless specified otherwise for critical fitments like snap-fits. PDF Resources & Technical Guides
You can access detailed guides and full tolerance tables through these technical document repositories:
PolTolerances Guide: A detailed 4-page overview of ISO 20457 and DIN 16742 including classification tables.
Standard Preview: An official abstract and sample pages of the ISO 20457:2018 Standard.
Engineering Guidelines: Practical application guides from manufacturers like OKW Gehäusesysteme showing how they apply TG6 to their thermoplastic products. PolTolerances en ISO-20457 (DIN 16742) - Scribd
Here’s a clear, professional write-up on ISO 20457 and its tolerance tables, suitable for inclusion in a technical document, training material, or engineering summary.
In the world of mechanical engineering and precision manufacturing, standards are the bedrock of quality. Among the myriad of ISO standards, ISO 20457 plays a specific and vital role in ensuring that complex machinery operates smoothly and reliably. For engineers and procurement officers, accessing the ISO 20457 tolerance table PDF is often a critical step in the design and verification process.
This article explores the scope of ISO 20457, the importance of its tolerance tables, and how to interpret the data found within these essential documents.
Understanding where ISO 20457 fits in the standards landscape helps justify its use to colleagues.
| Standard | Material Focus | Key Feature | |----------|----------------|--------------| | ISO 20457 | Plastics (moulded) | PT grades, parting line allowances | | ISO 286 | Metals / machined | IT grades, very tight | | ISO 2768 (general tolerances) | Metals & plastics (vague) | Often too tight for plastics | | DIN 16901 | Old German standard for plastics | Replaced by ISO 20457 in 2020 |
If your company still uses DIN 16901 or a custom “shop standard,” transitioning to ISO 20457 reduces confusion with international suppliers.
The iso 20457 tolerance table pdf is more than a grid of numbers; it is a strategic tool for balancing cost and quality. By understanding the three tolerance classes (Fine, Medium, Coarse) and knowing how to navigate the linear and angular tables, you can produce drawings that are both professional and manufacturable.
To recap:
Keep a legitimate copy of ISO 20457:2018 on your digital shelf, and you will never again guess whether a "±0.5mm" is appropriate for a 2-meter-long part.
Disclaimer: This article is for informational purposes. Always refer to the official ISO 20457:2018 document for legally binding tolerance values and definitions.
The ISO 20457 standard (which succeeded DIN 16742) provides a standardized framework for tolerances and acceptance conditions for plastic molded parts. It defines tolerance groups (TG) ranging from TG1 to TG9, where lower numbers indicate higher precision. For many standard industrial thermoplastics, TG6 is the commonly used baseline for general tolerances. Key Tolerance Tables and Documents
Because ISO 20457 is a copyrighted standard, full official tables are typically accessed through authorized distributors or summarized by manufacturers. You can find detailed overviews and downloadable PDF guides at the following sources:
PolTolerances Guide (Makrolar): A comprehensive 28-page PDF that includes detailed tolerance tables, explanations of dimensional deviations, and the relationship between ISO 20457 and DIN 16742.
OKW Gehäusesysteme Tolerance Overview: Provides a concise technical data sheet focusing on TG6 tolerances for various nominal dimensions.
ISO Official Store: The definitive source to purchase and download the official ISO 20457:2018 PDF for full compliance.
Super Ingenuity Template Library: Offers downloadable quality and tolerance templates, including Excel-based CTQ (Critical to Quality) feature tables and 2D note blocks for ISO 20457-TG6. Understanding the Tolerance Groups (TG)
The tolerance applied to a part depends on both the chosen Tolerance Group and the Nominal Dimension (the size of the feature). Nominal Dimension (mm) TG4 (High Precision) TG6 (Standard/Technical) TG8 (General Purpose) > 10 to 18 > 18 to 30
Note: These values are typical approximations for linear dimensions; refer to the official standard for the full matrix covering all dimensions and specific material groups. Selection Process
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
For general thermoplastics, the standard typically defaults to Tolerance Group 6 (TG6) unless otherwise specified.
Application: General tolerances (Series 1) apply to explicitly drawn dimensions that lack individual tolerance indications.
Typical Note: Engineering drawings often include the note: General tolerances ISO 20457 – TG6. ISO 20457 Tolerance Table Overview
The standard uses two main tables to determine the applicable tolerance: INTERNATIONAL STANDARD ISO 20457
standard (which replaced the older DIN 16901) provides a comprehensive system for determining manufacturing tolerances for plastic molded parts. It classifies tolerances into Tolerance Groups (TG)
based on material properties (such as shrinkage and stiffness) and the manufacturing process used. www.makrolar.eu Tolerance Tables Overview
While the full standard is a paid document, several engineering resources provide summarized tables for common applications. Tolerance Groups (TG1–TG9)
: These range from high precision (TG1) to normal production (TG9). For standard thermoplastics in injection molding, is a frequently used baseline for general tolerances. Dimensional Categories iso 20457 tolerance table pdf
: Tolerances are assigned based on the nominal dimension of the part (e.g., < 1mm, 1–6mm, 6–30mm, etc.). Material Influence
: High-shrinkage materials (like POM or PA6) typically require larger tolerance values compared to low-shrinkage materials (like ABS or PC). OKW Gehäusesysteme Reference Documents & PDF Guides
You can find detailed summaries and excerpts of the tolerance tables in the following resources: Engineering Guides PolTolerances Guide
provides a detailed 18-page technical overview of ISO 20457/DIN 16742, explaining how to calculate and apply these values. Industry Application OKW Enclosures provides a Tolerances PDF that specifies how they apply to their thermoplastic injection molded parts. Standard Samples iTeh Standards Sample PDF of ISO 20457:2018
which includes the first few pages and Table 8 (General Tolerances). Detailed Overviews
: For a more visual breakdown of the material categories and tolerance groups, Online Documentation on understanding plastic part tolerances. OKW Gehäusesysteme TOLERANCES
ISO 20457:2018 standard (often referenced alongside ) defines the tolerances and acceptance conditions for plastic molded parts. It replaces the older DIN 16742 standard to provide a global unified guide for designers and manufacturers to manage the unique dimensional, shape, and positional deviations inherent in polymer cooling and shrinkage. www.makrolar.eu Key Components of ISO 20457 Tolerance Groups (TG):
The standard categorizes dimensions into groups (TG1 to TG9), where is the most common industry standard for thermoplastics. Dimensional Deviations:
Unlike metal parts, plastic tolerances must account for processing shrinkage, tool binding, and material properties. Geometrical Tolerancing:
It includes specifications for surface profiles, angular dimensions, and tool offsets (parting lines). OKW Gehäusesysteme Reference Documents & Tables
While the full standard is a paid document, several manufacturers and technical forums provide summary tables and PDF guides: PolTolerances Guide (PDF):
A detailed explanation of how to apply ISO 20457 and DIN 16742, including shrinkage equations, can be found on Tolerance Overview (TG6):
A practical summary of the TG6 group values used for injection molding is available through technical resources like OKW Tolerances ISO Official Standard: The full official text and thumbnails for ISO 20457:2018 are available on the ISO Online Browsing Platform Templates & Snippets:
For engineers needing quick note blocks or Excel templates for CTQ (Critical to Quality) features, Super Ingenuity provides downloadable quality templates. OKW Gehäusesysteme Common Applications Primary Interest Part Designers
Specifying functionally required tolerances based on polymer behavior. Toolmakers Agreeing on shrinkage compensation and tool contour limits. Quality Engineers Applying acceptance criteria in production control plans. Tolerance Group (TG) table breakdown for a particular nominal dimension range? TOLERANCES
ISO 20457 is the current international standard for determining manufacturing tolerances of plastic molded parts. It replaces older standards like ISO 8062 and is closely aligned with the German DIN 16742. This standard is vital for designers and manufacturers to agree on achievable precision without driving up costs through unnecessary accuracy requirements. Key Tolerance Groups (TG)
Unlike metal parts, plastics have high shrinkage and warpage, requiring specific "Tolerance Groups" (TG) based on material properties and manufacturing effort.
TG4 (Fine): Used for high-precision components like internal gears or small medical parts. TG5 (Medium): Typical for functional housing parts.
TG6 (Coarse): Standard for non-critical consumer products or packaging. ISO 20457 Tolerance Table Overview The ISO 20457 tolerance table, found within the
The following table provides general capability ranges based on the part's nominal dimensions (size) and the selected tolerance grade: Nominal Dimension (mm) TG4 (Fine) TG5 (Medium) TG6 (Coarse) Up to 1 mm 1 to 3 mm 3 to 6 mm 6 to 10 mm 10 to 18 mm 18 to 30 mm 30 to 50 mm 50 to 80 mm 80 to 120 mm 120 to 180 mm 180 to 250 mm Critical Requirements for ISO 20457 Callouts
Simply stating "ISO 20457" on a drawing is insufficient. For a tolerance to be enforceable, the design documentation must include:
Tolerance Grade (TGx): Specifying the exact group (e.g., TG6).
Conditioning: Standard measurement temperature (usually 23°C) and humidity (50% RH).
Measurement Method: Specifying tools like a CMM (Coordinate Measuring Machine) or Optical Measurement Systems.
Datum System: Clear reference points to ensure repeatable results. Why ISO 20457 vs. ISO 2768?
Understanding the ISO 20457 Tolerance Table The ISO 20457 standard, which officially replaced the older German standard DIN 16742, is the global benchmark for specifying dimensional and geometrical tolerances of plastic molded parts.
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
In the manufacturing of plastic parts, applying standard metal tolerances (like ISO 2768) is not practical. Plastics behave differently during and after cooling.
The ISO 20457 Standard defines acceptable manufacturing deviations to:
Establish realistic limits for part sizes based on manufacturing effort and tooling.
Prevent over-specification, which leads to unnecessarily expensive molds and high scrap rates.
Set uniform general tolerances when no individual tolerance is specified directly on the drawing.
📐 Tolerance Class TG6: The Most Common Injection Molding Standard TOLERANCES
The ISO 20457 standard, which replaces the older DIN 16742, is the primary international guideline for determining tolerances of plastic molded parts. Unlike metal components, plastic parts undergo significant shrinkage and environmental changes, making standard rigid-body tolerance chains (like ISO 286) often unsuitable. Core Tolerance System (Tolerance Groups)
ISO 20457 uses Tolerance Groups (TG) to define the achievable accuracy based on the manufacturing process and material properties.
TG6 (Standard Baseline): The most common tolerance group for standard industrial injection molding.
TG4 (High Precision): Used for Critical-to-Quality (CTQ) dimensions, such as snap-fits or bearing housings, though it requires more expensive tooling and process control.
General Tolerances: If no individual tolerance is specified on a drawing, the standard applies "general tolerances" based on the selected TG to ensure all features are controlled. Factors Affecting Tolerance Selection In the world of mechanical engineering and precision
To develop a piece or select the correct table value, you must consider:
The standard provides tolerance tables categorized by the Type of Dimension and the Material Group.