MSP;
Thanks, I wasn't too sure whether the slug would contact the threads, being as the peak of the threads would still be at least a couple thousandths larger than the bore. That is asking too much precision with a slug though, I presume.
Markus;
If I get to my Walmart soon, I'll try to get the stock # for you...these were of course, meant to clamp onto the vent rib of a shotgun barrel.