Hi there!
This looks like the Series 380 or Series 385 channel balance. The best match will depend on the depth of the bottom shoe so you'll have to measure as shown below. Your metal channel length is odd as it should measure 25" based on the stamp. You may want to double-check just to be safe.
If it's indeed 24", you must weigh the window sash on a scale to determine the proper stamp option. There's a chart under the product description on the S380 and S385 store pages that you can use as a reference.
