channel sash balance

A contractor from Redwood City, Ca. says:
I need sash balances for 4 aluminum dual glazed windows that I believe to be viking from 1988.

Two of the windows measure 18" tall and have channels with 1520 stamped on them and two smaller markings that appear to be si but wear makes it difficult to be sure. This channel measures 16" of metal plus shoe and top. I need to replace 4 of these. The other 2 window sashes measure 30 wide by 24 tall and the balances are missing. When i try to identify the channels I have from the 18" tall sashes, it appears to be S-350. I assume that the channel balances would be similar for all windows in the house, since they are the same brand. The only discrepancy between the S-350 in the catalog and the one I have is that the width of the shoe is 15/16 (This would be in the space between the sash and the jamb. it would not be the wings which do measure 15/16). This is closer in size to the 15-005 than the 15-004 on the S-350. I suppose this could be 30 years of wear.

Is this enough information to order replacements for all four windows? Do we need to consider weight?
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Tom from SWISCO responded:
Thanks for posting. I agree, your shoe depth was likely 1" originally, but wore down 1/16" over the years.

You can place your order whenever you wish directly from our site. The 1520 option is likely correct, but you can always weigh your sash on a scale to be 100% sure.
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