hello,
is something missing on the hub ? , cap?
Pascal
Looks like you have a Bearing Buddy installed. There should be a rubber cover over the center where the grease zerk is located. Something like this may be what you want:
https://www.etrailer.com/Accessories-and-Parts/Bearing-Buddy/BB23B.html
Be sure to order the correct diameter for your installation. If you have any questions contact etrailer.com. They are super helpful and will get you squared away in no time.
Marc
Yep. You can order on amazon. Keeps grease from kicking up from the bearing buddy to your hull while trailering.