Window channel balance Replacement

Thanks for writing in. It appears the bottom nylon fitting, or shoe, lacks wings or 'side tabs'. Is that the same case for the top fitting also? I believe so but it's a bit tough to tell from that angle. If both attachments lack wings, then I believe you need either a S351-28 or S390-28. The only difference between these two channel balances is the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe'. See the diagram below for reference. Compare both with your old hardware to see what matches best. In either case, for a stamp option choose 2740.

Comparison of the S351 and S390 balance shoes.

For the other window, if you give me the height of visible glass in the window sash, I can tell you the length of the balance you need; and if it is a window otherwise identical to your other one and in the same house, it is likely also either the Series 351 or Series 390. However I can't 100% guarantee that--furthermore, without seeing the balance we have no way of knowing what stamp option you should select. The stamp option indicates the strength of the balance. It's important to get right. Removing the sash is the only way to see the stamp; therefore it is in your best interest to remove the balances anyways just to be safe. Let me know if you have further questions.