Granite square rulers :BoHai square rulers are widely used for accurately checking the X-Y-Z axes on almost all machines/tools and coordinate measuring machines
  With a side surface lying in the horizontal position and an indicator in the spindle, the X and Y axes can be checked for 90 degrees squareness. With the square standing in a vertical position, by an indicator tracing along the vertical edge of the square, the perpendicularity of Z axis can be checked conveniently. And by tracing along the top edge of the square, it will check the parallelism of the table in the X and Y axes to the spindle. Our standards mainly according to GB87-85, GGG-P-4630, DIN876, JIS-B510, ISO-DP8512 and so on. This item are available in grades”000”"00" and"0", Manufactured from carefully selected black granite.