Storm window part

It's a little plastic tab with what looks like a small screw or tension coil. The windows tilt kind of sideways and you pull them out.  I attached a picture of one on an intact (but dirty,  sorry) window showing the tab that's missing. It's just on the upper part of the window.  Could I please get help identifying this part? I believe these storm windows were installed in the 70s or 80s but not sure.  They appear to be aluminum.  White.  

That seems to be it,  I'm not sure if the screw on the side is part of the tab or not. Either way it's the closest thing I've found! Thank you!