Clutch type diffs vs others

[kpjo4]

I know the differences between a torsen/helical, open, viscious, and clutch type and how they operate but my question is when you open up a pumpkin how can you immediately identify it's a clutch type vs the others? I'm asking because I'm in the market to buy one and would like to be able to spot the difference when I see it in person in a differential. I tried searching on google and other forums including this one but seem to not be able to pull up anything.