Can you help me understand how this gaskets fits in place? If you lookup model number du486 (jenn-air) and scroll down to number 18. This should be a large round rubber gasket with a slit, on one side, all the way aroound. Does this slit have any purpose? If I just place the gasket on the bottom it is too large for the diameter of the openiing. So my question is does it go over the outer edge and then you screw it down or does it go on the underside and then you screw it down? There is also a smaller ring pretty close to the outer egde on the underside of the plate. Does it go there?