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Casey from SWISCO responded:
April 5, 2019
Your balance looks like either our S351-23 or S390-23 channel balance for non-tilt windows. The difference between the series 351 and series 390 balances lies in the shoe.The series 351 channel balance has the 15-002 shoe while the series 390 channel balance has the 15-001 shoe. The 15-001 shoe is 1/8" larger from front to back. 
Comparison of the S351 and S390 balance shoes.
Once you determine which series of balance you need, you'll want to weigh the sash and use the sash weight range/stamp option chart pictured beneath that balance to determine which spring strength option you should select. |
