The overall length is 26 inches, 25 with just the metal. The only numbers on it are 24 9 then not sure if it is BS1 or 8S1 with one end white and the other brown.
It is a bathroom window
Tom from SWISCO responded:
April 13, 2018
I would start by looking at our S385-25 channel balance, I think you'll find this is a good match. Your stamp is an outdated system, so I would recommend weighing your sash on a scale and referring to the chart on the S385-25 store page to confirm the best match.