27 3 AN Caldwell

I am confident we can help, but that stamp is not an identifier. It just indicates the strength. If you can remove the balance from the window and show us the nylon attachments on both ends, we'll do our best to help from there.

They are, thank you. Start by comparing to the S380-28 or S385-28 Channel Balances. The only difference between these two balances is the shoe depth. See below. See which matches what you have. For a stamp option choose 2730.

Comparison of the S378, S380 and S385 balance shoes.