Nilfisk Meteor vacuum cleaner dust container cyclone insert. This goes in the dust container to use the cyclone effect to separate the dust into the dust container and allow free passage of the air. It helps to protect the foam Pre-Filter and H12 HEPA filter behind it.
As it's light, maximise the saving on postage and buy a couple of Pre-Filters that protect the cartridge filter and the whole set of filters! See in related parts below.
At the moment, standard postage within Australia is capped at a maximum of $20!