Wrong spiral balance

A quick learner from Maspeth, NY says:
I ordered this part item no. S900-12. It's the wrong part. I spoke with someone from your company and they told me to take a picture and send it to you. The part you sent is on the right. The spiral spring is not as long as the original I need the part that's in the middle.

Please let me know if you have this part. Also let me know how I should return the wrong part.
User submitted image of their window hardware.
Profile picture of Paul
Paul from SWISCO responded:
It looks like your old balance is much larger than the S900-12. The key measurement when determining length is the size of the outer tube, not the inside spring. If you have an undamaged version of this balance, I would use that as reference. I would suspect the diameter is thicker at 9/16", as well, which would make our Series 600 a closer match. You will need to confirm the length of the other tube to find the proper match.
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