Felt fibre glass, mil-i, 22023, type 1, class 4, w/synthetic rubber skin, 1 in. Thk material, 17-1/2 in. O/a w by 22-1/2 in. O/a lg, 4-7/16 in. W by 10-1/2 in. Lg aperture, two 1-3/4 in. Diameter holes 8-3/4 in. C to c on w and 6-1/8 in. From edge on lg