BS 1806 standard for O-rings
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.