2 x 4000. The felt hub seal used on all the XK120, 140 & 150 stub axles and on a variety of other classics. If this seal is found to be thicker than required for your purposes, the felt can easily have layers peeled off until width is suitable for your job

This relates to the original Jaguar part number C615.

Fits into retainer ring that inserts , raised rim lip outwards (creating a cup) SEE: 4001.  which is against the back of the hub against raised face of stub axle carrier.

NOTE : you may wish to try immersing the felt in thick oil for a few hours, wring excess out and then grease both sides, to provide a better seal.