[Arran]

I would suggest acquiring a thread gauge, it will remove any ambiguity about what the thread pitch might be. Most modern bicycle axle nuts are metric I think, the threads used in 1920s radios are definitely going to be Imperial threads, unless it's a set from France or something. There was another weird thread pitch that was used on optical and scientific equipment sometimes, but I doubt whether Westinghouse would have used that.
Regards
Arran