Pops, what you're describing sounds like what nitro was talking about. I had the first one of those here in Seattle in my shop about 10-12 years ago. The tip of the "gun" or handle lightly welds to the panel (no studs or other attaching devices). Depending on who's unit it is there is either a built in slide hammer in that handle or there is a prybar kind of arrangement as part of the handle, either way the idea is to pull out the dent.

If you look at the pic I posted above you'll see some nail like studs sticking to the panel. The stud welder attaches them to the metal and then you attach a slide hammer with a chuck like end on it to grip the welded stud for pulling. The stud then is snapped off, or cut close and finish ground depending on how hot you welded it.