Window balancers single hung window

Thanks for posting. This looks like either a Series 351 or Series 390 Channel Balance. The only difference between these two balance Series is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See below. Measure your old balances' shoes to see what matches best. 

Comparison of the S351 and S390 balance shoes.

The balances stamped 28-3 should have a metal channel length (not including the nylon attachments at the ends) of 29". Please confirm. If so, these are either the S351-29 or S390-29, depending on the shoe depth as explained above. For a stamp option, choose 2830. 

The balances stamped 24-2 should have a 25" metal channel length, and are either the S351-25 or S390-25. For a stamp option choose 2420. Let me know if you have further questions.