Mick,
Thanks for chiming in with that bit of info about the K7. Your theory makes sense except for one thing. If the digit was the year of manufacture, then that means there must be K2s, K3s, K4s, etc, on the go as well. That might be the case but I haven't heard of any. Mind you, I hadn't heard of the K7 until I got this hub!
I've looked at the 1930s online catalogues for Sturmey hubs and can't find any mention of a K7 there. If what you're saying is that the K7 stamped on the hub refers only to a date and not a model name, then it all ties in.
Anyone else able to back up Mick's dating theory with some hard evidence?
Bruce
Dundee
Scotland