Lock-Top Damper Size(in)	Fits INSIDE Flue Widths of(in)	Fits INSIDE Flue Lengths of(in)	Outside Base Dimensions(in)	Height of Damper When Open(in)	Cross Sectional Area of Opening(sq in)
8 x 8	6 - 9	6 - 9	10 x 10	8	49
8 x 13	6 - 9 1/2	9 - 12 1/2	10 x 13	8 1/2	70
8 x 17	6 - 9	14 - 17 1/2	10 x 18	7 1/2	105
13 x 13	9 - 12 1/2	9 - 12 1/2	13 x 13	9	100
13 x 17	9 - 12 1/2	14 - 17 1/2	13 x 18	7 3/4	150
17 x 17	14 - 17 1/2	14 - 17 1/2	18 1/4 x 18 1/4	7 1/4	225