What top sash guide do I need?

Looking at your photos, the first part to pop in my head was the 18-166. This looks very similar in terms of design, and you can see that it is 7/8" across the top and 5/8" across the bottom. However, those are only two dimensions among many that you have to check. You need to go over each measurement we show on the 18-166 store page to confirm they match your existing top sash guide. That will tell you for sure if it will work.