I am trying to identify the correct replacement part for my window. The part number starts BC4 6-23(?) with a date of 1-87. This is a double hung window. The panes are 28 1/2"W x 16"H. It looks like this might be the 637 replacement.
Paul from SWISCO responded:
December 22, 2016
I agree. Based on your stamp of "6#27," I recommend our 24-637.