Paella between the glass blinds. This part fits through a glass hole at the top window allowing the control strings to exit the blind. It also holds the blind to the top of the window frame. There is a threading screw part and a type of nut part. The screw part is 1/4 inch and fits the hole precisely. Hope this helps. Pella says they no longer make this part. It's from a 20 year old window.
Thanks,
Clay