An odd solution to a nonexistent problem
These adapters were included with the canisters equipped with electric wands. Because of the oval shape of the electric wand, necessary to facilitate the electrical wiring on the back, customers would sometimes have a hard time with slotting the electric wand and bare floor brush on the side of the machine in the "Storage and Carrying" position. It was probably included with your SUB20 brush because of the male electrical connection on the end of the wand interfering with the cuff of the SUB20 brush. Either they readjusted the size of the wand, or made adjustments to future machines to eliminate this issue because they haven't been included with any of the Miele electric canisters we've sold in the last 4 years that I've been a Miele dealer.