Well, I use one quite often, and its not an iron at all, what you have there is missing a part, there is a steel rod that is bent at a 90 degree angle that fits though that rectangular slot, that ends in a wedge, what its used for is counting paper
what you do is slide that metal bit until its tight against your stack of paper, say, 100 sheets, then you tighten the handle, now you just slide it though a larger stack of paper and it will separate out 100 sheets.
Very useful tool