I lost a couple at first and Spartan took care of it. In my opinion this is the worst thing I've seen in my Spartan chassis. The design could be better. Then again, if everything else works that great and this is all I can complain about, I guess I should count my blessings.
What I did to eliminate the walking of the top hats was bend the tabs on the brackets. Squeeze each pair together so that they exert more pressure on the top hats and they will stop walking away on you.
This is the one (and only one

) area where Freightliner had a better idea with their positive retaining nut system.