I have a 1950's Unisaw, and bought one of the Delta knurled replacement arbor nuts. I'm not sure if it's the 36-659 or 36-660, but both the nut and the arbor have left-hand threads.
Anyway, although the original arbor nut threads on and off quite easily, the replacement doesn't. Like I can't get it on at all. Are the arbor threads different on the older saws? Maybe I just need to find a die and run the threads... what's the thread size?