Need help identifying part

Hello there!

Thank you for contacting us. My recommendation is either the S380-27 or S385-27 based on what I see here. The best match ultimately comes down to the depth of the bottom fitting as shown below.

Your stamp is a little odd though. You'll need to weigh the window sash on a scale and refer to the chart under the product description on the S380-27 and S385-27 store pages to determine the accordant strength option.

Comparison of the S378, S380 and S385 balance shoes.