I went the same as the thread on the end of the crank. 10x1.25mm. I did not need to though. The last couple of these I copied the CRRC 40 system. It forces everythng to come out straight if you pay attention.

The internal hub taper section is a near 100% contact fit. The straight section of the hub that the fits over the cranksfaft is a push fit. The prop stud then fits into a push fit cylinderical hole on the other end of the hub. The stud is threaded on the inside and threads over the end of the crankshaft. The hub is sandwiched between the crank and the stud. If your hub blank is true in all dimensions and you dial it in when you turn it around in the lathe, the two sides should be super straight after you bore the holes. It is a lot of trouble but I hate shaky engines.