Window balance replacement parts

On the 24" length, the number is 2340. On the 16" length, the number is 1540. From your diagram I determined this is 371 series. I have 6 windows that would require both sides to be replaced, which should be 12 balances.These are the 24" length. The 16" length I have 3 windows that require both sides to be replaced, which should be 6 balances. I was told the extra part in the picture needs to be with each balance, which attaches to the sash. I need 18 of these.From the pictures please verify if I am correct.