A modular screening panel in which the apertures in the screening surface extend through the surface and the shape of the aperture parallel the plane of the panel surface varies with the depth of the aperture so that as the surface wears the visible shape of the aperture changes. The apertures can be any convenient shape at the surface but at the depth which means the worn panel needs replacing the shape is distinctly different to the shape of the apertures in a new or partly worn panel.