Sheet metal pinch clamps (?)

[preston]

YOu know those little clamps that hold two pieces of sheet metal together flush? They look really useful for aligning and welding sheetmetal except that they imply a minimum gap of 0.032" between the metal pieces to allow their "key" to fit through the metal.

Everything I've ever been taught is you want your gap to be as minimal as possible. Do good fabricators ever use these or are they for hack repairs?

I've never used them due to the "gap", but they do look really nice for holding everything in place while you tack, not to mention a .032 gap on each side would make the filler piece a lot easier to cut since you have .064 leeway.

I'm inclined to think the magnetic versions would be better although of course its difficult to weld anywhere near a magnet and they're obviously no good on aluminum.

edit - these things - http://www.eastwood.com/review/product/list/id/56/