26 4 CN Caldwell

Thanks for posting. I believe this balance might be either our S380-27 or S385-27. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the illustration below for reference. Compare both with your old hardware to see what matches best. For a stamp option choose 2640.

Comparison of the S378, S380 and S385 balance shoes.