Copper screw terminal strip.
Be careful not to confuse the cross-section of the electrical cable with its diameter.
The section represents the copper surface in cross-section. Expressed in mm², the cable cross-section is equal to pi*R² (pi = 3.14, R being the radius of the circle)
So for a flexible electric cable with a cross-section of 25 mm², 25=3.14*R², i.e. 25/3.14=R², so the radius is equal to 2.82 mm. The diameter of the electrical cable will be equal to 2 times the radius, or 5.64 mm.