The reduced size of openings in fine screens may require that the screening surfaces be manually cleaned with brushes or steam every six to eight weeks. The various types of fine screens may be catagorized and differentiated by the way that they are positioned relative to the incoming flow, the screening medium utilized, or the cleaning mechanism employed. Many filter screens rely on the screenings themselves to enhance solids removal. One variation of the filter screen uses two step-shaped sets of thin vertical plates to form the screening grid. Most designs employ roller chains and sprockets to convey the screening belts/panels. Static screens use a stationary, inclined screen deck that acts as a sieve to remove solids from liquids. A variation of the static screen is the vibrating screen. Vibrating screens are much more effective than static screens in applications that require handling greasy or sticky solids.