I will try to explain with pics, as I do know the English words for it. It is a mix of this =>
...with this =>
Range is 0-48mm. For example you could use it well with tightening 1",1-1/8", 1-1/4" threaded headsets. They won't damage the lockring as conventional tools do, as they fit tight (you put pressure on them). You can put quite a lot force on them because of leverage. They wont hurt your hands much by doing so, because of the rubber cover.
My 'ZangenschlÃ¼ssel' is the 250mm long one. There also excist a 180 and a 300. The 1st of course having a smaller range, the later a wider range. There are also isolated ones and ones with dual compound (more) rubber.