Part identification on channel balance window

This part broke on the window itself. The channel balance appears to be in working order, but the part on the window broke, and so it doesn't "catch" the balance when the window is being lowered. I looked on your website, but I'm not sure what this part is called, or whether it can be replaced.

Thank you!

I received the parts (18-166) a couple of days ago and installed yesterday, they were perfect, exactly the pieces I needed. Thanks for the help!