Replacement for balance

A quick learner from Farmington, CT says:
This is a (1936) wood double hung window. The coil is 3/8" and the channel in the sash appears to be 1/2".
Would a series 400 spiral balance work? (The description says for aluminum windows). With a #32 bracket?

And could you please tell me how to measure the length for the replacement. Do I need to remove the old one first?

Thank you very much!
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Paul from SWISCO responded:

Thanks for your inquiry. Before we can begin recommending any replacement hardware to you, we would need to see the parts  removed from the window. Could you do that for us? Once you have the balance measure the balance from the top to the bottom metal right before getting the color bearing tip. With this extra information, we can provide you with our feedback. 

A quick learner from Farmington, CT says:
Photos attached. Length is 25" from top to beginning of grey tip.

Thanks for your help.
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Paul from SWISCO responded:

Thanks! Mill works that made wood windows back in the 30's would use a 5/8" diameter Series 500 spiral balance, in addition to a a bracket like our 17-012. I would bet your old balance once had an outer tube diameter of 5/8" as well, but it just worn off. You don't want to base the diameter off the inside spring diameter. 

For your wood sashes, I recommend our S500-25 red tip balance with a 17-012 bracket. These brackets hook on the balance spiral. Let me know if you have any additional questions.

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