Thanks for posting! I see that your channel is stamped with the number "14 3." I recommend the 14-3 option, then. This can carry a window sash weight range of 8 through 12 pounds. Does your sash's weight fall within that range? Weigh your sash and let me know!
Please keep in mind that the weight range information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
In that case, you would want the option of 14-1. This can carry a window sash weight range of 5 through 8 pounds.
approx weight = 7 pounds.