Milgard balance stamp option

A quick learner says:
Hi, My milgard window balancers have a stamp 3 S.I. and I had assumed it means 6kg, so I bought the 3020 for S395-31. Turns out that it is not strong enough to hold my window. Could you recommend the right strength to me?
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Tom from SWISCO responded:
I've never seen a stamp like that. Are you sure that's all there is? Maybe some of it has faded.

Either way, I recommend weighing your sash on a scale and referring to the chart we have on the S395-31 store page. That is the best way to determine exactly what option would work for you.
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