Hello there I am doing my windows now and that part is a component piece for (If I remember well) the front mounting piece that goes
thru window hole and allows you to put a mounting bolt. The piece you have shown is just one part the other is a metal washer looking thing
that is theaded in the middle and that plastic part connects to it. I will try and find a way to photo to help illustrate what I am trying to say
It is important for window mounting. Cuda Joy