Nilfisk 50mm industrial vacuum cleaner hose rubber protection rings.
They're for protecting hoses from rough surfaces, for example in engineering workshops. Slides on to the hose and then grips.
Please note the rings in the photograph are the 32mm make. The 50mm size is exaclty the same but larger.
At the moment, as postage is capped at a maximum of $25, maximise the saving on postage and buy some of the related parts below, such as dustbags and a new hose, or a new floor tool and some other accessory!