Vintage Yarn Weights

I’m reading through some vintage patterns from the Red Cross, and they always give the yarn weight like this:
4/14 sock yarn
4/8, 4/4, or 3/6 sweater yarn
4/10 (from a muffler pattern)

I tried searching on Yarndex and using Google, but no luck. Anyone have an idea what that translates to in contemporary yarn weight? I think I can make a pretty good guess, but some of you have encyclopedic knowledge of all things knitting, so I figured it was worth asking.