A gyration point can be replaced by a screw axis denoted by a number, n, where the angle of rotation is 360 ∘ ∘ n . The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. For example, 2 1 is a 180° (twofold) rotation followed by a translation of ⁠ 1 / 2 ⁠ of the lattice vector. 3 1 is a 120° (threefold) rotation followed by a translation of ⁠ 1 / 3 ⁠ of the lattice vector. The possible screw axes are: 2 1, 3 1, 3 2, 4 1, 4 2, 4 3, 6 1, 6 2, 6 3, 6 4, and 6 5.