About the BS 1806 standard for O-rings

The BS 1806 standard for O-rings is produced by the British Standards Institution. The BS 1806 specification describes 464 O-rings. Each size is designated with a dash number and can be described using two values: the inside diameter and diameter of the cross-section. The BS 1806 standard includes all of the 5 main cross section groups in AS 568 A standard plus extra sizes in the ¹⁄₄ inch nominal cross-section group.

In contrast to the AS 568 Ainch system, the nominal and physical dimensions of metric O-rings match precisely. That is, a 1 mm O-ring will have a cross-section of 1 mm. The space that is being filled must be about 10% to 15% smaller than the cross-section of the O-ring in order for O-ring to seal properly.

Sizes within the BS 1806 standard for O-rings

This table includes O-ring sizes there were included in earlier versions of the BS 1806 standard, but later eliminated.