A probable metal piece of a cartwheel that was probably the one shown in this photo by Thames Discovery being used as a mooring feature:
https://twitter.com/ThamesDiscovery/status/1308086159688560640/photo/1
Now resting against some timbers on the foreshore below Sea Containers House, Southbank, London.
200 photos taken in September 2020 with a Sony a6000 and processed in Reality Capture.