Window balance

Hello, thanks for posting! It looks like you could have either our Series 385 or Series 380. The difference between the Series 380 and the Series 385 lies in the depth of the shoe. Take a look at the picture below for more detail. Once you have determined this dimension you should be able to select the appropriate balance. 

I recommend double checking the length of your channel balance, as a 27-C stamp would typically indicate a 28" long metal channel (disregarding the plastic attachments). 

Comparison of the S378, S380 and S385 balance shoes.