The Joker was first produced around 1985. These cams had two moving cam lobes and a third fixed cam surface in opposition. The stem was a flexible spring design which would allow the stem to bend in shallow placements without breaking. Pulling the trigger was uncomfortable and took a little bit of strength!
I had one of these, a #2 I believe, on my rack back in 1992. I found it to be useful on the soft sandstone in the Garden of the Gods outside Colorado Springs, Colorado due to the fat surface area of the fixed cam.