Thread adapter for a fan switch

Guys - I've got a 350 Chevy in my 54 Kaiser project car and working out issues as I go. One of them is some kind of adapter that will go into the cylinder head (I removed the plug). The fan thermostat switch has a smaller thread size than the plug I took out and hoping there's something I can buy to make it all fit.
Would anyone know what size to get? This switch has SAE (?) threads. Thanks!

Take the plug and the switch to your local automotive or hardware store, they will set you up with an adapter that matches both thread sizes and pitch.

Will do, thanks!

Tompkins on Delaware will be able to get you what you need if you can't find it at a parts or hardware store.

Thanks, Ryan, good to know!