I have an O-360-A1F6D in my RV-4. It uses RHM40E spark plugs. Some of my RV O-360 friends have REM40E plugs. I see that the RHM is a 3/4-20 thread, and the REM is a 5/8-24 thread. Out of curiosity, why would there be two different thread sizes for an O-360?
Thanks,
Another friend pointed that out to me. I'm still wondering why there would be different shielding sizes...