Abstract: A glazing bead adapted to secure a second, larger thickness of insulated window in a window frame designed to normally receive a first, smaller thickness of insulated window. The glazing bead comprises a plastic extrusion having a resilient, arcuate wall member which engages the window and/or the window frame. Extending outwardly from the wall member is a folded leg member which is inserted between the window and the window frame, thereby compressing it and urging a locking flange on the folded leg member into engagement with the glazing lip on the window frame to secure the glazing bead and the window in place in the window frame. When the glazing bead is snapped into place, the arcuate wall member is compressed and thus resiliently urges said locking flange laterally towards and into engagement with said glazing lip on said window frame. This compression of the resilient wall member also tends to effectuate a seal between it and the window.