weight of the sash balance for single hung window. channel length is 27"

Thanks for posting! Yes, the 26 4, would be the 2640 stamp option for our balances. Although, it would be a good idea to double check your sash weight to ensure that it falls between the weight range indicated on the website.

The stamp cannot be used to identify the balance series you need. If you are unsure of what you have, I'll need to see a photo of the balance remove from the window. I'd specifically be looking to see the attachments from the top and bottom of the assembly.