This is the base plate that is connected to the bottom of the stainless steel rods. It does not come with that rubber ring that is attached to the underside of it, so definitely keep that! Don't chuck it out.
There are two sizes available, so make sure you are gettting the correct one.
This particular one will fit the following OASE Filtoclear models
OASE Filtoclear 12000, 16000, 20000 and 30000
it will NOT fit the following models
3000, 6000, 11000 or 15000. We have that in the spare parts section too :)
OASE part number 21539