Westfalia T2 Bay Front Seat Headrest Joint Hole Cover/Sleeve/plug Pair - Sold as a pair. They are identical to the original covers. They are made of the same material as original ABS plastic.
The measurement for the inside diametre of the plug is 22.2mm, and the depth of this plug is 29.0mm.
The measurement for the outside diametre for the top ring is 39.1mm, and the outside diametre for the base tube is 25mm.
Hope this is helpful.