Window balances

A handy person from Oxnard, CA says:
Hi, I have about a dozen windows that need the balances replaced. I have included pictures of my current balances. The window measurements is 35" x 58.5". I did measure the metal rail of the balance and it was 35" x 1/2". I narrowed it down to series 380 or 385...I think. Can you help determine which I need? Also, I haven't noticed anything saying these are sold as a pair so I am assuming that I need to buy two for every window am I correct?

Thank you so much for your help!

User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
I can't tell just by eyeballing these pictures what you have, no. You will have to measure the shoe and use your best judgement to determine if it's a 15-004 or the 15-005, for the Series 385 and Series 380 respectively.
15-004 and 15-005
It is best to replace both balances at the same time, yes.
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