Duct Size	A	B
6 inch	3"	13"
8 inch	3"	16"
10 inch	3"	19"
12 inch	3"	21"
14 inch	3"	24"
16 inch	3"	27"
18 inch	3"	30"
20 inch	3"	33"
24 inch	3"	39"

 

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