Sash support ID

A home owner from Kenosha, Wisconsin says:
Trying to ID this sash support. The channel is 16" end-to-end, and it is stamped "15 D", and also stamped "Fiberlux Mt Vernon, N.Y.".

It appears to be your 350 series, but am unsure of the weight - is it 15 pounds?

Thanks!

Dale Lovejoy
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hey, Dave. Typically, a stamp of 15 D corresponds to our 1540 option. You should weigh your sash on a scale just to be sure, though.
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