S159

Hey there. Good question. The Series 159 spring weights are a little tricky since they come in X-1/2 pound increments. You always want to be within 1 pound of the actual sash weight. So in your case, use the S159-08 8.5 pound springs, one on each side of the sash. That will get you 17 pounds of support, close enough to the 16.2 pound weight.