Sphere Precision and Grade

Spheres in Tray

itpstyli only uses spheres with the highest of grades, which are in the range of grade 3 to 5. A ball's grade is decided by the roundness and accuracy of the sphere diameter.

Grade ø deviation Roundness

± 0.13µm



± 0.08µm


Nominal Ball Diameter The diameter value used to identify the ball size
ø Deviation The difference between the largest and smallest diameters of one ball
Deviation Roundness The greatest radial distance in any radial plane between a sphere circumscribed around the ball surface and any point on the ball surface.

During calibration, it establishes the centerpoint of the ball so diameter tolerances are almost insignificant for 3D metrology. The roundness deviation, however, does greatly affect measurements. Using a higher ball grade (lower number) reduces the problems of roundness deviation.

itpstyli not only offers an extensive range of standard styli, but also offers the Design Your Own styli option where you can create a custom stylus that fits your specific application.