The balance number will be stamped or printed on the metal channel which determines the spring tension. The length of the balance is determined by measuring the metal channel only and do not include the plastic end bracket guides in the measurement. This balance channel width is 9/16 in. x 5/8 in. D. Make sure your balance matches the specs of this balance before ordering as well as any specific end brackets.Aluminum metal channel for strengthDesigned for longer life when you change balances on both sides of the sashProvides smoother operation when you change balances on both sides of the sashFor seasonshield, alenco and other brands of windows