choke dash knob mod

All of the switches I have seen use the same 1/8" NPT fitting, which is pretty common for things like oil pressure sending units, hydraulic brake light switches and such. Any of those listed in the posts above should work. I'd go for the NAPA one since you can probably find it in stock locally.

In the event that you need some sort of brass tee or adapter, they will also have those and will often let you rummage through the drawers until you find the right one. At least they used to do that...