Made of fine-grained, black, metrology grade granite, GMT Six-Face Granite Master Squares are used to check squareness or parallelism of any artefact or structure. Master Squares have six finished faces. The two surfaces of the square are parallel to one another and perpendicular to the four sides.

They have through-holes for weight reduction and ease of handling. GMT 6-Face Granite Master Squares are ideal for accurately checking the X-Y-Z axes. Best dimensional reference for CNC machine tools and coordinate measuring machines.

When the square is in the horizontal position, you can check for squareness of the X and Y axes. To check the perpendicularity of the Z-axis, with the square in the vertical position, you have to trace along the vertical edge of the square with a gage. To check the parallelism of the workpiece to the table, trace along the top edge of the square placed vertically, along the X and Y axes.


  • Six-Face Granite Master Squares are made from world-famous Indian Black Granite, which is best suited for Metrology.
  • They have two large faces and four edges as working surfaces.
  • In addition, they have holes to reduce their weight. These holes are used for handling also.
  • GMT uses extremely tight tolerances in the manufacture of Granite Master Squares.
  • These master squares can be used to accurately inspect the X-Y-Z axes on CNC machine tools and Coordinate Measuring Machines.
  • They can also be used on any workpiece that requires the checking of squareness or parallelism.
  • GMT granite squares are available in custom sizes and configurations and can be made to the Standards requested by the customer.

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