29 3 A channel balance

Thanks for writing in! Your channel balances appear to the Series 395 Channel Balance with a winged top guide and wingless bottom shoe. The specific replacement you'll need is the S395-30.

Since your balance is stamped with a 29 3, I believe you can use the 2930 stamp option. Although, you may want to confirm that the weight of your sash falls between 16 to 23 lbs.