What series balancer is this

A quick learner from Pearl River La says:

I need 2 balances like this, the window isn't tempered, you have to pull the clips out on the side of the window to release the sash to change it, what's the cost for 2 Thanks!

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Bob from SWISCO responded:

Thanks for writing in. Take a look at our S770-40. Just make sure that all the dimensions and specifications match your old balance. I believe your stamp code of 3940 might conform to our stamp option of 40D, which is for a window sash in the weight of 27 through 32 lbs, but to be safe, I think it would be best to weigh your window sash to make sure it falls exactly within this range. All prices will be listed on the product page. Let us know if you have any other questions. 

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