Ok,I should have said most hemi 4-speeds I have had or repaired ( more than 50) had a magnet, the factory part had a 5/16 dia by 3/4 long past the pipe plug end, sticking out in the oil? piece of steel that was magnatized, not a ceramic or rare earth magnet. If you use rare earth magnets go with samarian cobalt, more stable in high temp applications.