Can you identify the part that I need to order

Hey there!

Thanks for reaching out to us. We're happy to look further into this. Before we can confirm, can you show us a photo of the inside of the balance's metal channel where the innerspring connects to the pulley mechanism? That'd be located in the middle of the channel. It looks like your spring may be damaged or missing so you'll have to use an undamaged balance as a reference. Can you also measure the bottom shoe as shown below and tell us what you find? 

Profile view of a winged balance attachment

Thank you kindly! Based on this photo and the fact that the shoe is 1" deep, you'd definitely want the S380-27. The stamp printed on the metal channel is too faded to make out though. You could check the balance on the other side of the window to see if that one has an intact stamp. If it doesn't, you'll have to weigh the window sash on a scale and refer to the chart under the product description on the S380-27 store page to determine the appropriate stamp option.