A handy person from stanley north carolina says:
February 5, 2015
I am replacing a balancer for a customer. it is stamped as a 20-32 and I do not see that as a option. should I use 2030 or 2040
Tom from SWISCO responded:
February 6, 2015
I'm not sure! That is an odd stamp. I recommend weighing the sash on a scale and comparing what you get to the chart listed on the S351-21 store page. That is the best way to determine what option you need.