[thecj3man]

The plug is 7/8" diameter on a 650 and 20 tpi.It will be a 60 degree thread,but I think it's BSC (cycle-thread),not a Unified thread ;although there's not a big difference.

7/8"x 20 tpi UNEF (Unified extra-fine aircraft thread) would be close enough.

I boogered up the threads in my crank with a new hex plug. I ordered a 7/8 NEF tap from mcmaster-carr and it worked like a charm to clean the threads up.