Granite Master Square


Made of fine black, metrology grade granite, the GMT 6-Face Granite Master Squares are used to check squareness or parallelism of any artefact or structure. Master squares have 6 finished faces . One large square face is flat and perpendicular to the four sides, which are parallel and perpendicular to one another.

We grind and lap the working surfaces so that they are parallel to each other and polish the remaining sides. They are provided with 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. With the square in the vertical position, you have to trace along the vertical edge of the square with a gage to check the perpendicularity of the Z axis. Trace  along the top edge of the square while in the vertical position, to check parallelism to the table in the X and Y axes.


  • 6-Face Granite Master Squares have two large faces and four edges flat, square and parallel to each other.
  • In addition, they have holes, to reduce their weight. These holes are used for handling also.
  • Furthermore, GMT granite squares are available in custom sizes and configurations.
  • GMT uses extremely tight tolerances in the manufacture of Granite Master Squares
  • As they ae made from world famous Indian Black Granite, they are best suited for Metrology.
  • For accurate inspection of the X-Y-Z axes on CNC machine tools and coordinate measuring machines.
  • Also can be used on any work that requires the checking of squareness or parallelism.

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