Tom from SWISCO responded:
September 15, 2016
Thanks for posting. The stamp option is a code that denotes how much weight two balances on either side of the sash, working together, can support. Your original stamp reads "18 4," which usually corresponds to our 1840 option. That said, you can always weigh your sash on a scale to confirm. We have a chart on the S350-19 store page showing how much weight each option can support.
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