Channel Balance Compatibility

A home owner from Edison, NJ says:
As recommended, I have ordered two Series 730 Channel Balances with option codes 2230 and 2240. I am not sure what these option codes mean. My existing channel balances have the numbers 22305 and 22405 stamped on them. The one with 22405 which goes on the left side of the window doesn't have the bottom plastic accessory. Otherwise, it looks identical to the one with 22305 (with the exception of spring length) which goes on the right side of the window. The ones that I was shipped both look identical with each having the bottom plastic accessory. However, one of them has 2230 and the other has 2240 stamped on them. (Also, the one with 2230 has shorter spring than the other). I am confused. All I know is that the left balance is not supposed to have that bottom plastic accessory. In addition, I see a bump on both of them an inch from the bottom end as shown in the figure. This is something that I do not see on the existing ones. I am not sure if it creates a problem during installation. Please help.
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Donna from SWISCO responded:
S730-23 with stamp option 2230 is designed for sashes weighing 12 through 19 pounds and the 2240 stamp option is for a window sash that weighs 19 through 23 pounds.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.

To determine the proper strength balance, remove the window sash and place it on a scale.
If the balances you are replacing are original to the window the manufacturer may have intended the two different stamp options for the same sash.
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