Window Lawson channel balance

Hello there. Is the metal channel, not including the nylon attachments at both ends, 30" long? If so this is either an S380-30 or S385-30. The only difference between these two channel balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the diagram below for reference. Compare both with your old balance to see what matches best. The stamp in your photo reads 2920; this is what you will choose as a new stamp option, which designates the calibration of the balance. Let me know if you have further questions.

Comparison of the S378, S380 and S385 balance shoes.