This item has not been available from Jaguar for quite sometime. There should be two on my car securing the carpeted cover to the ‘metal tray’ that houses the convertible top pump/relays & the battery is underneath - they have never been there for the 15 years that I’ve owned the car.
By chance, whilst removing the rear bumper to replace a broken reflex lens, I found one of these turnbuckle studs in the bottom of the passenger’s side rear wing. I approached a local design/drafting/engineering & 3D printing guy & now I no longer have missing turnbuckle struts:
Originally, I reckon Jaguar had these made in 3 different colours: light grey, dark grey & sisal to match varying trim colour combinations. The one the guy has printed so far for me is in a similar grey to the original one I found. There is a relatively small cost in modelling (scanning) the original item but the printing of each item, due to the small size, is quite low. I’m pleased with the results: