▁unit ▁cell . ▁The ▁d ▁gli de ▁is ▁often ▁called ▁the ▁diam ond ▁gli de ▁plane ▁as ▁it ▁features ▁in ▁the ▁diam ond ▁structure . ▁, ▁, ▁or ▁ ▁gli de ▁translation ▁along ▁half ▁the ▁lattice ▁vector ▁of ▁this ▁face ▁ ▁gli de ▁translation ▁along ▁with ▁half ▁a ▁face ▁diagonal ▁ ▁gli de ▁plan es ▁with ▁translation ▁along ▁a ▁quarter ▁of ▁a ▁face ▁diagonal . ▁ ▁two ▁gl ides ▁with ▁the ▁same ▁gli de ▁plane ▁and ▁translation ▁along ▁two ▁( d ifferent ) ▁half - l attice ▁vectors . ▁ ▁A ▁g yr ation ▁point ▁can ▁be ▁replaced ▁by ▁a ▁sc rew ▁axis ▁denoted ▁by ▁a ▁number , ▁n , ▁where ▁the ▁angle ▁of ▁rotation ▁is ▁ ▁. ▁The ▁degree ▁of ▁translation ▁is ▁then ▁added ▁as ▁a ▁sub script ▁showing ▁how ▁far ▁along ▁the ▁axis ▁the ▁translation ▁is , ▁as ▁a ▁portion ▁of ▁the ▁parallel ▁lattice ▁vector . ▁ ▁For ▁example , ▁ 2 1 ▁is ▁a ▁ 1 8 0 ° ▁( two fold ) ▁rotation ▁followed ▁by ▁a ▁translation ▁of ▁ ½ ▁of ▁the ▁lattice ▁vector . ▁ 3 1 ▁is ▁a ▁ 1 2 0 ° ▁( three fold ) ▁rotation ▁followed ▁by ▁a ▁translation ▁of ▁ ⅓ ▁of ▁the ▁lattice ▁vector . ▁ ▁The ▁possible ▁sc rew ▁axes ▁are : ▁ 2 1 , ▁ 3 1 , ▁ 3 2 , ▁ 4 1 , ▁ 4 2 , ▁ 4 3 , ▁ 6 1 , ▁ 6 2 , ▁ 6 3 , ▁ 6 4