White = primary Yellow = secondary
Back in the olden days (80's) they used to state in the VFG or ERSA that a horizontal sock indicated 30kts.
However by the late 80's changes appeared with the ERSA (I think) stating 20 or 25kts for an all out on some socks. So it appeared you could have 2 different rated socks around the country. At about the same time the govt. documents stopped stating the rating of the various socks.
This became known as the era of CYA (cover your arse) so after allowing a non standardised system to evolve the regulator went silent on the subject.
M