G.M. temp sensors are normally supplied with the EM-4 systems. For air cooled engines the Bosch sensor is supplied in place of the G.M. coolant temp sensor.
G.M. sensors are 3/8 npt.
Bosch CHT sensor thread is 10mm x 1. (1 thread per mm).
These are made here at Racetech. These should be used only if the G.M. sensors cannot be fitted.
Bosch air and water temp sensors are another option. These use 12 X 1.5 mm threads, sealing with a crush washer not included.
Bosch water temp left, air temp right
Size comparison of available temperature sensors. Left to right, 1/8 NPT Dale, 3/8 NPT GM, 12 X 1.5 Metric Bosch