Michael, here is a short take on what is involved with the Skillet Oven. What the patent is showing is an annular RAISED "base" if you will. Picture a "high" base waffle iron. It has a "socket", or lug on one side, and a cut out for the handle of the skillet oven opposite of that. The skillet oven rests on a "ledge" inside this raised annular base. This traps the heat inside the area for quicker cooking. Note the "ball member" and handle do not carry the weight of the oven, that's the purpose of the "ledge" inside the raised base. I would guess this piece to be several inches in height.
The "insert" is just that. It goes inside the oven (w/ means of attachment" to cook other foods . The adaptor ring you have does not go with the oven. It appears to be an adaptor plate for a stove that would have several other plates to allow different size openings (ie: 6", 8", ect).
Edit to add: In other words, the skillet oven fits inside the adaptor ring. ;)