I believe this is a top sash guide for a channel balancer

Hello, thank you for posting,

Unfortunately your exact top sash guide is no longer made. We have suggested the 18-066 to other customers, however we cannot make any guarantees it would work as a replacement. Some sashes are made with a type of contour built into the framing that may not allow them to install properly on the sash.

With that said, take a look over the dimensions and design to see if you believe this could be a fit for you. Let us know what you think and if you have any additional questions! 

Front view of 18-066

Side view of 18-066