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