broken part inside window sash

A quick learner from Hanover, PA says:
August 29, 2019
We moved into our new house in Hanover, PA which was built in 2004 by Bob Ward Company. Our windows are now 15 years old and some of them have broken parts inside the window sash. The broken part is shown in the pictures above. There is a spring that is 15 inches long which is on a rod that is 27.25 inches long with a string inside. These broken parts don't allow the window to stay up without propping it open. The bottom window tilts in and lifts out but the top window is immobile. Can you please help us to identify this part so that we can get a replacement?
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Bob from SWISCO responded:
September 4, 2019

Thanks for writing in. This old rod balance isn't made anymore, but this particular type can be replaced with our Series 770 Channel Balance. Measure the length of the rod to determine the correct length to select. You will need to weigh your window sash to obtain the correct stamp option. Let me know if you have any other questions.
A quick learner from Hanover, PA says:
September 5, 2019
Thank you for that information. I measured the length of the rod to be 27" but what do you mean by "weigh your window sash to obtain the correct stamp option"?
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Tom from SWISCO responded:
September 6, 2019

Stamp options indicate the calibration of the spring; in other words, they're an indicator of how much weight two balances can support when working together. Your old balance doesn't have a stamp option so you'll have to do some homework to figure out the calibration of these new springs.

To do this, you will need to remove the sash from the window and place it on a scale to get the weight. You Any common bathroom scale will do. You'll then refer to the chart we show on the S770-27 store page to determine the proper option.
27" Series 770 Balance
27" Series 770 Balance
S770-27
$12.70
How to replace a tilt-window channel balance.
How to replace a tilt-window channel balance.
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