Granite Squares
AC Metrology supplies black granite squares to BS 939:2007 in grades AA and A, from 200 x 200mm up to 500 x 500mm, including master squares for laboratory reference use and lighter tri squares. They’re used for checking squareness on surface plates, machine tools and CMMs, and each square is supplied with a UKAS calibration certificate from an accredited laboratory.
What granite squares are used for
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Checking squareness and perpendicularity of machine tool and CMM axes
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Inspecting components and fixtures on a surface plate
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Verifying 90-degree features on machined parts
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Acting as a reference when checking other squares
Grades and standard sizes
Grade AA is the laboratory grade, with the tightest squareness tolerances, for standards rooms, calibration work and master reference use. Grade A is the inspection grade, for quality departments, toolrooms and machine set-up. A common approach is to keep a grade AA square to check the grade A squares used day to day.
Squareness tolerances to BS 939:2007. Larger squares can be supplied with lifting or lightening holes for safer handling, and custom sizes are available.
Granite tri squares
A granite tri square is a lighter alternative to a block square, with one large flat face and two narrow edges finished flat and square to each other. It covers squareness checks across X, Y and Z axes at a lower weight, which makes it easier to handle on larger machines and CMMs.
Used alongside
Granite squares are used alongside a granite surface plate, granite straight edges and parallels.
Granite square FAQs
What grades of granite square do you supply?
We supply granite squares to BS 939:2007 in grade AA, the laboratory grade, and grade A, the inspection grade. Grade AA has the tighter squareness tolerances.
What sizes of granite square are available?
Standard sizes run from 200 x 200 x 25mm to 500 x 500 x 50mm. Custom sizes are available, and larger squares can have lifting or lightening holes.
Do granite squares come with a calibration certificate?
Yes. Each granite square is supplied with a UKAS calibration certificate from an accredited laboratory, showing its measured squareness.
Why use a granite square rather than steel?
Granite is stable, non-magnetic and doesn’t rust, and it’s less affected by handling heat than steel. When it’s knocked it chips rather than raising a burr, so damage is easy to spot.
What is a granite tri square?
A granite tri square is a triangular granite square with one large flat face and two narrow edges finished flat and square to each other. It’s a lighter alternative to a block square for squareness checks on machine tools, CMMs and components.