I guess I am going to have to get to a shop and get some hands on knowledge, closest place is over an hour drive. I've only ever owned 2 and still don't think I quite get the "true rotary" thing. Does only the clamp itself spin? My whole shaft spins, has a threaded section that runs through a hole in the vertical arm. I am going to have to see if I can dig up my old vise and take a pict, you will see why I'm a little slow in the equipment terminology. The one I use now was a gift so have just learned to deal with it.