Use a small open end (10mm perhaps?) or crescent wrench to hold the stud that is spinning - there is a place on the other side of the bar that is flattened for this purpose.

Simply disconnecting my sway bar ends in Moab got me highest RTI score (832 I think) of any IFS truck in Moab and made running trails a whole lot easier. I have been told Calmini sway bars are the same diameter as what we have stock - can you confirm that and give your impressions if they really are stiffer?