Nice Hercules, I hope it cleans up well.
a Hercules B Type 4 - I picked up from somewhere that this hub was made by Brampton for Hercules (hence the B), but I'm not sure of the significance of the number 4 - it's a three speed.
Don't assume too much from the hub codes. I have a A type O hub. All I can tell you is that it is an alloy shell, a 3 speed, and is a 30's vintage. I think the letters and #'s denote more a time line and perhaps a gearing range more than anything else.