Sash top hook
Thanks for posting! The part you are searching for is what is referred to as a top sash guide. It hooks onto the balance top guide to make sure the balance is secure while traveling in the channel. Your top sash guide looks like it could be the 18-044. Carefully compare the dimensions of this part your existing hardware to confirm if this is the right replacement.
Your balances appear to be the 3/8" width Series 800 channel balance. These balances have the 19-007 top and and the 15-018 bottom, wingless attachments. For the balance stamped with the 28B, you'll need the S800-29. For the balance marked 23BF, you'll need the S800-24, however, I would recommend double checking the sash weight to determine the stamp. The 23B stamp is made to carry windows weighing 8 to 13lbs.
I would recommend double checking the width of your balances and the attachments to be sure that this is the balance series you'll need.
We do not carry a replacement for the sash stop you have here, unfortunately. The only stops we carry are parts 55-043 and 55-110, however, I do not believe they would work to replace your existing stops.
Let me know if you have any questions.