A combination square is a tool used for multiple purposes in woodworking, stonemasonry and metalworking. It is composed of a ruled blade and one or more interchangeable heads that may be affixed to it. The most common head is the standard or square head which is used to lay out or check right and 45 angles. In woodworking, the starting raw material is neither flat nor square, however, the end product such as a table must be flat and have corners and legs which are square. In metalworking, it is useful for a wide variety of layout and setup tasks. When used correctly, a fairly high degree of precision can be achieved. One use would be setting large items at the required angle in machine vices, where the long reach of the ruler and firm, heavy base aid the process. Invented by Laroy S. Starrett in 1878, the combination square continues to be a commonplace tool in home workshops, construction jobsites and metalworking
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