21 12 OL BSI

Question

Need to replace 8 block & tackle window balancers.  Sash weighs 35 pounds.  As noted in subject......channel is stamped 21 12 OL BSI.  Measurements of guides (top and bottom) in pictures.  These are single hung windows.  Thanks.

Emily · Accepted Answer

Hey there!

Based on what I see in your photos, my recommendation would be either our S351-22 or S390-22 channel balances. The crucial difference between these two parts is the depth of the bottom fitting so you'll need to measure as shown in the image below. I also recommend the 2170 strength option. A pair of balances with this stamp will support a sash weighing 34 to 37 pounds.

Comparison of the S351 and S390 balance shoes.