Files and scrapers are two common hand tools. Files are used for deburring, rounding sharp edges, filling corners and sharpening heavy tools. These tools come in many types, such as flat-tipped files, triangular files, square files, dog point files, round files, half-round files and more. A file set contains one or more types of file. Files come in different makes as well. Hard chrome plated files, for instance, are robust and best suited for working on hard pieces. Many top-end files have convenient wooden grips. A hand scraper is a tool with a single edge, used to scrape metal. A major application of scrapers is for frosting, or to create a shallow depression in precision ground surfaces, for oil films to maintain surface tension. A smoothly ground surface offers no means for oil to stick, and runs the risk of seizing of the bare metal. Hand scrapers are also used for other applications, such as to correct a metal sheet to fit a mating part, and to decorate a piece. Hand scrapers offer a higher level of accuracy and flatness compared to lapping or grinding. After developing an original prototype with a scraper, the accuracy may be transferred to other surfaces by grinding. Three-square scrapers are mostly used for cleaning, smoothing and deburring metals and bearings.