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Square countersunk screws are fasteners consisting of a threaded shank and a square-shaped or Scrulox socket head. More importantly, these screws have a countersunk head that allows them to be sunk in timer or sit flush in predrilled countersunk holes for a flat surface finish. Also known as Robertson screws, they require an appropriately sized square drive to screw and fasten materials together. Square countersunk screws are commonly made of stainless steel and are used in several industries, including electronics, machinery, engine, and furniture assembly.