'inlet cap'
This was more commonly seen on the chrome tops,rarely on D3.I think the idea was if using just to clean air or add fragrance the machine could run with this screen type cover without sucking in possible nearby curtains,etc.D2 held on with magnets,D3 should be friction fit.--There was also a rarely seen tool caddy to sit on chrome tops.I think 1 cord hook on D3 version,none on D2.(Many small chrome top ads show this cover in place so it doesn't look like just a vacuum until the demo.)