Product review (3 stars): The expensive, proprietary Jenn Air burner
I have this model burner. It is on a Jenn Air cook top downdraft model  now discontinued. The burner is a simple piece of metal nothing fancy, but it goes as high as $75 for some reason! They do NOT show what it looks like from the bottom or from angles anywhere on the internet, even on the manufacturers site. I am providing pictures of my old beat up leaking burner so you can tell what you need. The center hole (bottom) is 3/4 inch. There are pre-drilled screw-holes for the gas feed tube and for the igniter. There are nibs (I'll call them) like pimples of metal on the burner that fit into notches on the cook top plate so they can be twisted in snugly. The alternate cheaper burners may not have these notches/nibs and might be looser, but I've read that doesn't matter to function alright. It must all be some proprietary size, such a crock. The after market burners (cheaper) show some kind of silver metal tube coming out of them. Nowhere does it give exact (or any) specs as to the size of the bottom hole on those other burners. It's a conspiracy! They make it so you have to pay out the nose for this simple little piece of metal.
Only because they make such a secret about the dimensions, the alternate views and the PRICE of this thing, plus the fact that it rusts out (it should be stainless steel for this price) I give it 3 stars.