For most commercial applications, PT2 (fine) or PT3 (medium) are the default choices.
Select a TG based on cost and function. TG6 is generally considered the "standard" for conventional molding.
Crucially, the standard explicitly excludes certain features from these general tables—for example, chamfered edges of screw threads, or dimensions that directly affect assembly of critical safety components.
What or resin blend are you using?
The standard defines 10 Tolerance Groups, labeled .
An important distinction exists between and ISO 22081 . While both standards address general geometrical specifications, they serve different purposes. ISO 22081 specifies general geometrical tolerances using surface profile as a geometric feature—either without datums or with a datum system that blocks all non-redundant degrees of freedom. By contrast, ISO 20457 provides a distance-dependent tolerance zone width approach specifically designed for plastics, recognizing that shrinkage effects cause dimensional variation proportional to the distance between features. However, as noted by tolerance experts, ISO 20457 does not fully implement the distance-dependent approach consistently throughout the standard.
The standard provides a framework for specifying tolerances that balance the need for precision with the practical limitations of manufacturing processes. iso 20457 tolerance table pdf
The ISO 20457 tolerance table provides a detailed list of tolerances for various features, including:
A common mistake in engineering is applying metal machining standards (such as ISO 2768) directly to plastic injection molding. This approach creates major manufacturing issues because plastic parts exhibit: Polymers shrink anywhere from as they cool inside the mold cavity.
The tolerance standards applicable for metal parts cannot be adopted for plastic structures or can only be applied to a very limited extent, which is precisely why ISO 20457 was developed. Plastic part variation comes from material shrinkage, cooling rate, and process fluctuation—not just from mold steel precision. For most commercial applications, PT2 (fine) or PT3
Disclaimer: This post is for informational purposes. Always consult the latest official ISO standard for legal and quality-critical applications.
Standard measurement temperature (usually 23°C) and humidity (50% RH).
ISO 20457 places heavy emphasis on injection molded fittings. The tolerances here are tighter than for pipes because molds are machined to high precision. An important distinction exists between and ISO 22081