Simonton series 385 31" channel balance

A home owner from San Francisco CA says:
I need 8 Simonton series 385 31" Channel balances
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Bob from SWISCO responded:

Hello there. Note that the fittings on this balance lack 'wings', or side tabs. Therefore this is not a Series 385 , but a Series 390 or maybe Series 351 instead. The only difference between these two balances is the depth of the bottom nylon shoe, or 'heel-to-toe' measurement, so compare your old hardware with the illustration below to determine which you need. 

Make sure you're measuring just the length of the metal channel, not including the fittings, to determine the length you need. Finally, you'll need to choose a stamp option which indicates the balance's strength. Look for a stamp on the metal channel that shows this. If there is none, or you are uncertain of the stamp's meaning, weigh your window sash. You can then match that weight with one of the weight ranges listed alongside each stamp option under the product description on every balance's shop page.

Comparison of the S351 and S390 balance shoes.
Comparison of the S351 and S390 balance shoes.
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