Manhole Covers and Frames finish the top of the NAL STAKKAbox™ Access Chamber Range. They fit directly into or on top of the chambers and are bedded onto a layer of mortar. They usually finish flush with the surrounding surface level. The covers are manufactured from three different materials, - Ductile Iron, Composite, and Steel, all off which have unique benefits. All Covers conform to European Standard. EN 124 Standard : Loading Classes : A15, B125, C250, D400.