BS ISO 3601 sizes & tolerances
BS 1806 has been superseded by BS ISO 3601-1 (dimensions)
and BS ISO 3601-2 (housings), but BS 1806 is still widely
referenced by industry. The size codes in BS ISO 3601-1 (nonaerospace)
are, with a few exceptions, the same as BS 1806.
However, there are two tolerance bands, Class A and Class B,
with the tighter tolerances of Class A equating to BS 1806. Our
Chart 50 meets the Class A tolerances.
The A suffix size codes in BS 1806 (eg, 445A) do not appear as
standard sizes in BS ISO 3601-1, but have been retained in Chart
50 as they are still requested.