O-Ring Lexicon

Dimensional standards

Dimensional standards define the inner diameters and cord thicknesses with which O-rings are manufactured and designated. The most important are the metric series to ISO 3601 and the inch series to AS568.

What are dimensional standards?

A dimensional standard is a defined grid of inner diameter and cord thickness. It ensures that an O-ring can be clearly designated and reordered in the same geometry regardless of the manufacturer. Two major systems are in international use: the metric series to ISO 3601, in which inner diameter and cord thickness are given in millimetres, and the inch series to AS568, which is common on the American market. In addition, there are older national series such as DIN 3771, whose content has now largely been absorbed into ISO 3601.

Why dimensional standards matter for O-rings

For designers and buyers, a standard creates clarity. Anyone specifying an O-ring to ISO 3601 or AS568 describes the geometry with no room for misunderstanding. This avoids wrong orders, makes groove design easier and keeps spare parts reproducible for years. Particular care is needed when switching between inch and metric series: an inch cross-section rarely corresponds exactly to a metric value, so it is worth checking the table before every substitution.

The key points at a glance

Dimensional standards define inner diameter and cord thickness on a fixed grid.
Metric follows ISO 3601, inch follows AS568, and DIN 3771 has largely been absorbed into ISO.
A clear standard prevents wrong orders and ensures reproducible spare parts.

You'll find the complete dimension series in our O-ring tables. The applicable tolerances can be found in the corresponding overview.

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