Need 2 balancers

Hello there. It looks like you might have the S380-30, S385-30, or S378-30 Channel Balance. The only difference between these three balances is the 'depth' of the bottom nylon shoe. See below. Measure your old balance's shoe depth to see what matches best.

Comparison of the S378, S380 and S385 balance shoes.

You then have to choose a stamp option, which reflects the strength of the balance. If there's no stamp on the balance telling you this, the best thing to do is to weigh the window sash the balances support. You can then use that exact weigh to choose the right stamp option. Let me know if you have further questions.

While judging from this photo the shoe depth does appear greater than 1". But pictures of measuring tape are not always reliable, so double-and-triple check to be safe. If it is greater than 1", then it is an S385-30. My apologies, I should have noticed you already told me the sash weight! If it's 20 pounds, choose a stamp option of 1930. This indicates a balance that can support a sash in the weight range of 16 through 23 pounds. Let us know if you have further questions.