however the two that have captive nuts are small 13mm's on the chassis.
the big 19mm is the one that goes on the end of the anti roll bar through the TCA

if this just turns then the anti roll bar thread is stripped, not heard of this happening as its a big thread, but i suppose that its possible. you can pick 28mm cossy anti roll bars up for abut 20 quid so if you cant figure it out just cutting it off isnt the end of the world