In carpentry, a square or set square is a guide for establishing right angles (ninety-degree angles), usually made of metal and in the shape of a right triangle. A carpenter is a skilled craftsman who performs carpentry -- a wide range of woodworking that includes constructing buildings, furniture, and other large objects out of wood. ... For alternate meanings, such as the musical instrument, see triangle (disambiguation). ...

This Old House describes several types and uses of squares : [1]

See also:

• Try square
• Combination square
• Speed Square
• Steel Square