About the JIS B 2401 standard for O-rings

The JIS B 2401 standard for O-rings is produced by the Japanese Industrial Standard. The JIS B 2401 specification describes 1006 O-rings in three different groups: aerospace, general purpose, and traditional.

The aerospace group describes 367 O-rings and matches the ISO 3601-1 standard very closely (with a few additional sizes). Each size is designated by its dimension: ID × cross-section. Subsequent to the dimension, the letter A is appended to indicate use in aerospace applications.

The general purpose group describes 445 O-rings and matches the ISO 3601-1 standard very closely (with a few additional sizes). Each size is designated by its dimension: ID × cross-section. Subsequent to the dimension, the letter G is appended to indicate use in general purpose applications.

The traditional group describes 194 O-rings. Each size is designated by a letter followed by a nominal number. The letter indicates the intended application of the O-ring: P - dynamic; G - static; V - vacuum flange.

In contrast to the AS 568 A inch 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.