20" balancer

Hey Rick. Is the metal channel, not including the nylon attachments at both ends, 20" long? If so, this is either an S380-20 or S385-20 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe, or the 'heel-to-toe' measurement. See below. Measure your old balance's shoe depth to see what matches best.

Comparison of the S378, S380 and S385 balance shoes.

You also have to choose a stamp option, which reflects the strength of the balance. Look for a stamp somewhere on the metal channel that denotes this. If there is no stamp or you are unsure, weigh the window sash these balances support. You can use that exact weight to choose the proper stamp option.