24" single hung widow spring

Hello, thanks for posting! It looks like you could have either our Series 380 or Series 385. 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.

Comparison of the S378, S380 and S385 balance shoes.

I would recommend confirming the length of your channel balance, as a 2430 stamp would indicate to me a 25" long channel. (When determining this dimension, disregard the plastic attachments at either end).