Balance channel
I'm afraid I can't tell what you have based on these photos. In order to ID a good match for your balance, I will need to see a clear picture of both the top and bottom nylon fittings and the stamp printed on the metal channel.
If at all possible, please make sure that the balance you show us is whole and undamaged. If any pieces are broken off or missing then there's a good chance we won't be able to ID a match for you. When it comes to balances like this, the first parts to break off are usually the most important, so it would save us both a lot of trouble to use an undamaged version as a reference.
Thanks! Thanks for your photos. Based on what I see here, you have either our S351-25 or S390-25, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.
If there is no stamp printed on the metal channel, then you will have to weigh your sash on a scale to confirm the best stamp option. That's the only way to know how these springs ought to be calibrated. We have a chart on each balance store page that tells you exactly how much weight each option supports.
