Hi Doug,
I'm know I'm a bit late to this conversation by about 4 months but I used 12mm Rivnuts to mount my sway bar with no issues. I've found it to be a very handy tool and worth buying. I actually ended up getting two Rivnut tools, one ratchet type for larger Rivnuts and a Pop rivet type for smaller ones. You could say though I found the ratchet type tool a little counter intuitive when using upside down in cramped locations. I nearly ended up with a Rivnut tool permanently attached to the chassis as it was a pretty tight spot and when I went to unscrew the tool there wasn't enough clearance to fully extract the mandrel.
