More Symmetry 

The combination of rotation and inversion results in an inversion axis. The symbol is n (read nbar). This is called HermannMauguin notation. For n = 1, 1 is an inversion center. For n = 2, n is not used. This operation would be the same as a mirror, m. A 3 inversion axis is shown to the right. Below, compare a 

The diamond glide, d, is found only in F (face) or I (body) centered cells. The diamond glide consists of reflection followed by translation of 1/4 along two cell edges.

Below, compare the nglide (left) with the dglide (right): 
Screw Axes are a combination of rotation axes and translations. The symbols are: 2_{1} 3_{1} 3_{2} 4_{1} 4_{2} 4_{3} The symbols are of the form x_{y} 
x_{y}
The rotation is degrees. The translation is units along the screw axis. 
A twofold screw axis, 2_{1}, refers to a rotation of or 180 degrees, combined with a translation of along the screw axis. +1/2 indicates translation of +1/2 normal to the plane of the page. (2_{1}is read two sub one) 

A threefold screw axis, 3_{1}, refers to a rotation of or 120 degrees, combined with a translation of along the screw axis. 
A second operation of the 3_{1} results in the object translated by along the screw axis. 
A threefold screw axis, 3_{1}, refers to a rotation of or 120 degrees, combined with a translation of along the screw axis. 
A second operation of the 3_{2} results in the object translated by along the screw axis. 
Notice the result is a set of screws that turn in opposite directions. 
