Replacement window balances

Thanks for posting. Channel balance identification is based on the style of nylon attachments at both ends. This looks like either a Series 380 or Series 385 Channel Balance. The difference between these two balances is the depth of that bottom nylon attachment, what we call the shoe. The depth is the measurement from the shoe's 'heel' to the 'toe'. See the picture below for reference. Measure the depth of your old balance's shoe to determine which you need.

Comparison of the S380 and S385 balance shoes.

For the length, make sure to measure just the metal channel. Do not include the nylon attachments in the measurement. If this is indeed 27", then you'll need either the S380-27 or S385-27. Finally, you have to choose a stamp option. This designates the strength of the balance. Look for a stamp code on the metal channel that indicates the correct choice. If there is none, or you're unsure, just weigh the window sash that these channel balances support. On every channel balance's shop page, there is a chart under the product description that lists weight ranges for each stamp option. You can use that chart to see which stamp option is best for your window sash's exact weight. Let me know if you have further questions.