taco eater :
Durks77 from Greenland, NH United States
There is a slight bevel on the ring surface that is supposed to be facing up.
the rings are not marked and they fit in the slots both ways, but you can tell that you have it in the right orientation by squeezing and turning the ring. if it is upside down there will be resistance and if you got it right side up then it will be much smoother.
Hard to see it but if you squint real hard the chamfer is there! Will overheat if installed upside down.
Make sure you orient rings correctly!! 
