a rigid rectilinear frame comprising end members, side members perpendicular to the end members and at least two and not more than ten intermediate members spanning the frame between the side members, the end, side and intermediate members being arranged in a pattern;

a screen assembly covering the frame including an upper fine mesh screen, a blinding screen, below the fine mesh screen, of coarser mesh than the fine mesh screen and at least a pair of load bearing screens for the fine mesh and blinding screens, below the blinding screen, including a first support screen of coarser mesh than the blinding screen and a second support screen of coarser mesh than the first support screen; and

a layer of heat fusible plastic of the same pattern as the frame members dispersed between the screens thereby bonding the screens together and an adhesive on the frame members bonded to the heat fusible plastic and thereby bonding the screens to the frame members, areas between the frame members being substantially free of bonding material thereby increasing permeable area of the screen and increasing screening capacity;

the flow path through the screening assembly being through the fine mesh screen, through the blinding screen and then through the load bearing screens.