These are the plastic parts that attach to the sash.

Thanks for your interest in SWISCO. First, we would like for you to take a look at our 18-180 top sash guide. Next, the balance you are showing us here looks similar to our Series 380 balance with a 19-005 top shoe and 15-005 bottom shoe. You will need to know the length of the metal portion and the spring weight imprint on your balance in order to determine the proper balance to go with. Let us know how you made out.