Sash balancer for aluminum windows

I can tell that this is a Series 380 or Series 385 channel balance, specifically S380-23 or S385-23, based on the shape of the attachments shown below. To tell which balance you need, you should measure your shoe. The 1" shoe is for Series 380 and the Series 385 uses the 1-3/32" shoe. You may need option 2220 for a sash weighing 8 to 12 pounds, but you should weigh your window sash to check.