Black insert that goes into the channel balance guide

This is a very peculiar setup. Typically a channel balance for a non-tilt window is held in place by something called Top Sash Guides, which are essentially nylon stoppers in the top corners of the sash. Your window uses pivot bars instead. Pivot bars are typically for an entirely different purpose, and for windows that can tilt inward for cleaning. Apparently whoever installed these windows used whatever they had available. This oddity aisde, we still may be able to replace these pivot bars. See our 26-040 or 26-083. Please compare and see if either of these match what you need.