Duct Size	A	B
6 inch	8"	3"
8 inch	10"	3"
10 inch	12"	3"
12 inch	14"	3"
14 inch	16"	3"
16 inch	18"	3"
18 inch	20"	3"
20 inch	22"	3"
24 inch	26"	3"

 

Measure your specific application, then refer to the chart to select the appropriate damper size.