Is this nut on backwards?

slantsixdan said
Yup, it's backwards. That's not a castellated or "castle" nut, either. See here.

No, but as I said, the nut has a castellated part. I don't know what else you'd call it.

They go on the way it shows here (click on link), which is what slantsixdan and a few others have said: Slant 6 Exhaust Manifold Washers