No number on Balance

A quick learner from Illinois says:
I can not find a number my channel balance. It appears identical to the model S372-19. What are the various options 1810, 1820, 1830, 1840 mentioned? How do these options add too or change the balance?
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Paul from SWISCO responded:

The different options represent different strengths of the balance spring. Sometimes the numbers are very faint on the balance, look closely again to see if you see any markings. Sometimes the stamp will not exactly be one of our options. If that is the case, respond back here with the stamp you do find.

If there is no markings on your original balance we can still figure out what option you need by going by the weight of the window sash. To weigh your window sash, remove it from the window frame and weigh it on a simple scale like a bathroom scale. See this guide on how to remove the sash from the window frame.

A quick learner from Illinois says:
There is no number on my balance. My sash weighs 4 lbs; so which spring option do I need for the Model 372 channel balance? 1810, 1820, 1830, or 1840?
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Casey from SWISCO responded:
Stamp option 1810 would be the lightest strength balance for Series 372.
S372-19 with stamp 1810 will carry a window sash weight range of 5 through 8 lbs.

This information is based on 2 balances per sash. Suggested sash weights do not include the manufacturer's sash friction from use of weatherstripping. This friction should be verified by the manufacturer since all windows vary in sash friction due to manufacturing methods and weatherstrip types.
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