Help with balance

Thanks for posting. It looks like you have either an S380-30 or S385-30 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe. See below. Measure your old balance's shoe depth to see what matches best.

Comparison of the S378, S380 and S385 balance shoes.

You then have to choose a stamp option, which reflects the strength of the balance. If there's no stamp on the metal channel, weigh the window sash these balances support. You can use that exact weight to find the right stamp option. Let me know if you have questions.