We have four classic Jaguars that I do most of the repairs, servicing and restoration work on. Having the proper technical data on these cars has removed a lot of the mystery (but not all of it) in keeping them looking and operating their best. In addition to the owners manuals, I have found the Repair Operations Manuals and Parts Catalogues all help me in many ways to sort out the parts I need and be a smart buyer.
Attached is a picture of the Series I XJ6 Parts Catalogue, RTC9106, that I purchased on eBay for probably about $30.
The part you are asking about, part number C33025, is shown circled on page 22 64.
When armed with the correct technical data, like the Parts Catalogue for your Jaguar, sorting out most parts identifications is quick and easy.