i3 Mega headbed cork insulation holder

cork plate holder for Anycubic i3 Mega heatbed insulation. The aim was to cover the entire heatbed surface to its edges. Four of these parts are needed, mounted at each corner. The printed mounting holes need to be drilled to 3.5mm to fit the heatbed screws.
Inspired by https://www.thingiverse.com/thing:2753110