Proof?:
https://www.reddit.com/r/mikrotik/comments/qpqt5d/rb5009_rackmount_kit_seems_confusing_but_isnt/
https://www.reddit.com/r/mikrotik/comments/xbosbm/the_rb5009_rackmount_kit_just_about_works_in_a_10/
https://imgur.com/a/rb5009-10-rack-ears-hNUuCqo