This is the FUEL TANK LOCKING RING and SEAL
for the RANGE ROVER CLASSIC (1986 - 1991)
Land Rover Part Numbers : ARA 1501L and ARA 1502L
If you have been changing your sensor unit then it is usually best to replace the ring and seal at the same time.
FUEL SENSOR UNITS are available for units with or without the low fuel warning light, and for the extra 10 and 15 gallon tanks fitted to pick ups and station wagons