A used ball pin spigot, as fitted to the E Types MK2 Daimler V8 420 and the XJ's part number C15339 or C30952 (item 42 in the illustration) Good used condition and still loads of life left in it just yet.

You can get aftermarket reproduction ones for about £14.00

If you wanted to keep the original ball joint set up rather than use the aftermarket sealed units this might be of use as a spare or if you're on a budget and just want a good used part.