A handy person from The Villages, FL says:
November 30, 2015
Part is 1/2" wide and 28" long from a CWS window. The bottom sash is 34.5"wide and 30.5 tall and weighs 23 lbs.
Paul from SWISCO responded:
December 2, 2015
Thanks for posting! Looks like you have something like our S385-28 channel balance. This comes with a 19-005 nylon balance top and 15-004 (1-3/32" depth) bottom shoe pre-assembled. Please compare this hardware to your own to confirm that everything matches.
For the option, your old balance has a 27-5 stamp for a sash weighing 26 through 30 pounds. But you say your sash weighs 23 pounds, so I would recommend our 2740 option instead. This is for a sashes weighing 19 through 26 pounds.