In the first picture we see a disk perforated by drilled holes. These holes are in a one-piece metal disk that is placed between and centers the lower heater-glass tube and the upper oven-glass tube. This piece does not come out when the stem ring, O-ring, and metal oven-tube are removed.
It can only be removed/replaced by removing the top-cover.
The screen seen in the metal oven-tube is correctly placed. The two screens are not interchangeable.
Edited to add picture showing perforated disk that centers the upper and lower glass tubes and protects the heater coils.