Window balancers

A landlord from Fort Wayne, IN says:
I was unable to get a picture of the balancer removed. They have a series of letters going down the front of the cover that is A through F and the ones I took the picture of also has the number 8 on it. I checked a window that was the same size as the one I need the hardware for and it had the number 7 on it. The coil spring looks like the S152 spring.
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Bob from SWISCO responded:

Thanks for posting. This looks like a 15-177 Pivot Shoe, so yes, that is compatible with our Series 152 Coil Springs. I wouldn't rely on the numbers on the housing, as they often do not indicate the coil spring weight. You will need to check the coil springs themselves for stamped codes that indicate the recommended weight. If there are no stamped numbers or you are uncertain, provide us the exact weight of your window sash, and we'll figure out what you need.

A landlord from Fort Wayne, IN says:
The only marking I can find on the spring itself is the letter "C"
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Bob from SWISCO responded:

Some manufacturers use a letter system instead of numbers, but one can convert to the other. So it wouldn't surprise me if the 'C', being the third letter in the alphabet, translates to a spring weight of 3 lbs, which means you'd want to consider the S152-3. I can't be certain of this, however, so I would still weigh your window sash just to be safe. If you get that exact weight, then divide in half, that will tell you how much weight support you need on each side of the sash. For instance, if your sash weighed  24 lbs, that equals 12 lbs of support needed on either side of the sash, in which case you'd want an S152-9 and a S152-3 on both sides of the sash. 

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