Space symmetry operators: All point symmetry elements are included in the spatial symmetry, but there are also screw axes and glide planes.
Screw axis: Are the combination of a rotation with a parallel translation. They are named with the number indicating the rotational component (N=2, 3, 4 o 6) and a subindex indicating the translational component to the rotational component (τ) thus: 21 , 31 , 32 , 41 , 42 , 43 , 61 , 62 , 63 , 64 , 65.
The ratio τ/N indicates the translation to be performed parallel to the axis, after each sub-rotation (always counter clockwise).
Fig. 12. Screw axes from 2, 3, 4 y 6 rotation axes.
