My first thought when I saw the picture was a "key" for concrete forms. They are wedges that you pound or push down to tighten the forms. The forms are like panels or rails, all different sizes. Then after the concrete is poured, the key is knocked out with a hammer so that the forms can be pulled or pried off.
That's my first thought when I saw the picture. I know I've seen that before. I think it was something to do with concrete forms.