Graphic symbols for symmetry elements

Different graphic symbols are used to label symmetry axes normal to the plane of projection, symmetry axes in the plane of the figure, symmetry axes inclined to the plane of projection, symmetry planes normal to the plane of projection, and symmetry planes parallel to the plane of projection. These symbols are illustrated in Tables 9.3.1 to 9.3.5, respectively. 

Symmetry element (screw Graphic Translation in units of the Printed 

Twofold rotation axis Twofold screw axis 2 sub 1  

Threefold rotation axis Threefold screw axis 3 sub 1  

Fourfold rotation axis Fourfold screw axis 4 sub 1  

---