A window frame spacer/clip/lock

I do not really know the name of this part, nor the function. From the uploaded images, there is one image named "window-model-number" and that is the only sticker/label I can find from the window. And the window channel balance has a stamp "86 29-9 DA5 CMC 7". Other than that, no labels were found.
The part I am looking for is that white small plastic. It seems to be used as a spacer or clip on the side of the frame. I mistakenly broke a few of them when I was trying to replace the window channel balances. So I would like to know what it is. If you have it, that would be even better.