A original used valve collar for pretty much all the Jaguar XK engines, this was removed from a MK2 engine number BH5090 and part number C2159 (item 25 in the illustration) these were superseded by C27480 but don't ask me what the difference is!
Aftermarket reproduction ones are about £7 each but if you wanted an original used Jaguar specification item for your classic then this item might be for you.