Abstract: An arch casing bead having a mounting flange and a ground flange extending therefrom. The mounting flange includes a free edge and an edge proximate to a junction of the ground flange and the mounting flange. A notch is formed in the mounting flange extending from the free edge towards the ground flange. The notch defines an arcuate portion which is positioned proximate to the ground flange. A pair of spaced apart edges extend from the arcuate portion to the free edge defining a mouth of the notch. The notch facilitates arcuate deformation of the elongated casing bead without angularly deforming the ground flange.