peachtree windows 30 1/2 x 29 1/2 length of balance is 26 1/4

Hello, thank you for writing in. The stamp that you indicate tells us the necessary spring strength, but we will still need to determine what series you have. In order to do this we will need to see clear images of the attachments at either end of the channel. I'd also like to confirm the length of your balance. When determining this dimension, be sure to measure only the metal channel and disregard any attachments. 

Hi Mark. Based on the information you've provided, we suspect that you have our S745-26. However, the stamp you show is somewhat confusing, because usually a S745-26 would have a stamp starting with a "25". If the Series 745 looks right to you, then I recommend weighing your window sash and referring to the chart on the product page to identify the correct option.