True Inch sizes of O-ring

The Bristish and American sizes of O-ring are referred to as nominal inch sizes - this is because the true inch sizes refer to the size of the O-ring gland area.  There are however O-ring sizes that have been popular for many years which are based on an exact imperial size, so for example:

1/16" measures 1.59mm, not 1.78mm as per the BS1806 / AS568B standard


1/4" measures 6.35mm, not 6.99mm.

Exact inch sizes are not in any International Standard series, but they are sizes that are still requested - see Popular True Inch O-ring sizes under more information below.

More information:
Popular True Inch O-ring sizes

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