I just sent another question earlier.
I thought they were S351-25 but I think these are more like S390-25. Any rate the stamp still says 2490.
I would like to replace 4 of them.
Tom from SWISCO responded:
May 27, 2015
2490 is actually not a standard stamp for the S390-25, so you will need to weigh your sash. Then, refer to the chart of weights we have on the S390-25 store page to determine which option will best work with your sash weight.