29" channel balances

You are correct--since the top fitting has wings, or those 'side tabs' but the bottom shoe lacks them, this is most likely an S395-29. Just review the product description to confirm. Your stamp of 28-4 would confirm to our stamp option of 2840, which would suggest the sash weighs 23 through 28 pounds. Did you ever have trouble closing or keeping the window closed, prior to the balance failing? If so you might need stamp 2830 instead, which is for a window sash in the weight range of 16 through 23 pounds. However, if you've had no issue with the window's performance before the balances failed, we strongly recommend sticking with the original stamp option of 2840.