Part missing

Thanks for your post! The photo you've provided of the part is the window balance assembly. You have the 15-180 Coil Balance Shoe which uses the Series 190 Coil Balance Spring. The coil is attached to the shoe using the 33-073 screw and it is being anchored to the window track using the 15-186 Coil Balance Clip and 15-182 Balance Bushing.

Alternate image for 15-180

If you no longer have the original hardware, you'll need to weigh the window sash to confirm the correct springs for the window. The video tutorial below shows instructions on how to choose the coil.