I have two of those commercially sold extension leads, on a plastic drum/reel, which have multiple sockets on one face of the reel. The reels are mounted on a tubular metal frame which includes a handle to carry the reel. Clipped onto the tube, alongside the reel, is a plastic thingummy, which almost touches the side of the drum. The thingummy can be rotated around the tube, or slide up and down the tube, but what I have never been able to work out, is the purpose of the thingummy. What is it for? Both have this thingummy, despite being different makes.
