Please help me locate what window balance I need

Question

On the balance it says 27 4 BSI OL. I know what the numbers 27 and 4 are but I don't know what series I need. The plastic ends of the balance are hard to figure out. Thank you

Bob · Accepted Answer

Thanks for posting. This looks like either an S380-28 or S385-28 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. For a stamp option choose 2470.

Comparison of the S378, S380 and S385 balance shoes.