Please HElP me Identify

A home owner from 33325 says:
These were removed from the windows. They are broken but I think you can ascertain the part for purchase as replacement.

Wonder why the numbers are different.

Window broke due to plastic retainer peice deteriating over the years.

Your help is appreciated.
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Casey from SWISCO responded:


It looks like you have either our S351-30 , with a 15-002 bottom attachment, or S390-30 , with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. 

If these balances we're removed from the same window, the stamp number should have been the same. It's possible that someone replaced one of the balances with what they had on hand, which means one side of the window had more tension than the other. I would recommend weighing your window sash and following the chart under the product description on the balance product page to make sure you choose the correct spring strength option for your replacement balances.  Thank you!

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