Window Balance 26-4 HA2 CMC 24

Hey there! We should be able to help with this. Can you show us a photo of the inside of the metal channel where the innerspring connects to the pulley mechanism? I will do my best to help from there. 

Thanks so much! From what I see here, you want either the S380-27 or S385-27 channel balances. The best match depends on the depth of the bottom fitting though, so you'll have to measure as shown below. I also recommend the 2640 stamp option based on your old stamp. 

Comparison of the S380 and S385 balance shoes.