Paul from SWISCO responded:
February 25, 2015
Thank you! Don't worry, you should be okay. The "Z" is the manufacturer's in-house code and doesn't affect the weight of the spring. I know that's a little confusing, so if you want to confirm you can always weigh your sash. Two S800-16 balances with a stamp of 16B can carry a window sash weight range of 7 through 12 pounds. As long as your sash weight falls within that range, you have nothing to fear.
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