A quick learner from Cortlandt Manor says:
September 21, 2016
Looking for the replacement for balance # J23 5#27 9-85. One of the sash strings no longer goes back into balance. In turn window does not easily stay up when opened.
Paul from SWISCO responded:
September 26, 2016
Hello! Based on your stamp of "5#27," I recommend our 24-531 Andersen sash balance.