A C-shape (also CH in some books) is a designated, specifically controlled structural steel shape with outside square corners, 3x flat and perpendicular sides, hot-rolled to controlled structural dimensions and alignment in a series of patterns that are designated (US convention) by: nominal height of the web and weight per foot of the member. ALL dimensions are controlled during the hot-rolling: height of web, thickness of web and flanges at midpoint, angle of the two legs (usually 2.5 degrees) and shape of the end of the two legs.
A "U" shape is usually trimmed from a square tube steel with uniform and equal leg and web thicknesses, and a height based on the original square tube steel height. Each edge of each leg is usually ground off square and burrs removed. The corner is as it originally was from the original tube steel: rounded inside and outside.
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