1. Measure metal channel length. Do not include any attached ends.
2. Check number stamped on channel. The first two digits represents the channel length. The second two digits represent the sash weight. (e.g.: The number stamped on the balance is 3248, you would then order #57-32S48. With 57 referring to our series, followed by the length of the balance then the sash weight.)-Max Weight 75lbs.