Nilfisk GB833 three phase industrial vacuum cleaner pleated closely woven cotton main filter. The clear photo is an illustration of the filter using the Nilfisk GS83 cotton filter for an example. The less clear photo, shows an idea of how the filter looks on the frame. But I have only one.
At the moment, as postage is capped at a maximum of $20, maximise the saving on postage and buy some of the related parts below, such as dustbags and the other filters or a new hose or floor tool!