This is a nylon channel balance shoe or bottom guide. There is the larger upper portion, which is stationary, but there is a lower portion that pivots . The rivet in the picture is the axis of the pivot, and there is a spring to keep tension on it. It goes with cheap aluminum single pane windows of unknown brand and age. The shoe has a fin on one side that fits into a slot in the jamb. There are no markings on the part.
What on earth is this thing, can I get more of them, and what is the right way to replace them? If you can tell me who made these windows, it would be much-appreciated.
Thank you,
Rickey