The volume of a sphere is given by the following equation:

Where r is the radius that is equal to half the diameter. If the diameter is 6.6mm then the radius is:
![\frac{6.6\operatorname{mm}}{2}=3.3\operatorname{mm}]()
Then the volume of the sphere is given by:
![V=(4)/(3)\pi\cdot(3.3\operatorname{mm})^3=150.53mm^3]()
So the volume of the sphere is 150.53 cube milimeters.