Lyemance Damper Size(in)	Outside Base Dimensions(in)	Fits INSIDE Flue Widths of(in)	Fits INSIDE FLUE Lengths of(in)	Damper Height When Open(in)
8 x 8	9 1/4 x 9 1/4	6 1/2 - 8 1/2	6 1/2- 8 1/2	3 1/4
8 x 17	9 x 17 1/2	5 3/4 - 8 1/4	14 1/2- 16 1/2	5
9 x 13	9 1/2 x 13	6 1/4 - 8 1/2	8 1/8 - 12 1/8	4 1/4
12 x 16	12 5/8 x 16 1/8	9 1/4 - 12	12 3/4 - 15	5 1/4
13 x 13	13 x 13	10 - 12 1/2	10 - 12 1/2	5
13 x 18	12 3/4 x 18	10 - 12 1/2	15 1/2 - 17 1/2	5
17 x 17	18 x 18	15 - 17 1/2	15 - 17 1/2	6 1/2
12 Round	13 7/8	10 5/8 - 11 3/8	10 5/8 - 11 3/8	4 3/4