▁hole ▁is ▁too ▁small , ▁the ▁p enc il ▁cannot ▁be ▁inserted , ▁while ▁if ▁it ▁is ▁too ▁large , ▁the ▁tip ▁of ▁the ▁p enc il ▁repeatedly ▁will ▁break ▁off . ▁Pr ism ▁sh ar pen ers ▁may ▁be ▁right - ▁or ▁left - hand ed , ▁requiring ▁clock wise ▁or ▁counter - clock wise ▁rotation ▁of ▁the ▁p enc il ▁being ▁sh ar pen ed . ▁ ▁Linear ▁bla de ▁sh ar pen ers ▁▁ ▁Un like ▁pr ism ▁sh ar pen ers , ▁linear ▁bla de ▁sh ar pen ers ▁do ▁not ▁rotate ▁relative ▁to ▁the ▁p enc il ▁being ▁sh ar pen ed , ▁and ▁may ▁be ▁viewed ▁as ▁just ▁a ▁special ▁form ▁of ▁kn ife , ▁with ▁a ▁mechanical ▁guide ▁for ▁increased ▁safety ▁and ▁convenience . ▁Some ▁models ▁use ▁replace able ▁sh aving ▁raz or ▁bl ades , ▁while ▁others ▁have ▁perman ently - f itted ▁bl ades . ▁ ▁Linear ▁bla de ▁sh ar pen ers ▁may ▁require ▁more ▁skill , ▁but ▁they ▁allow ▁one ▁to ▁sh ar pen ▁the ▁tip ▁of ▁the ▁p enc il ▁into ▁any ▁desired ▁shape ▁and ▁angle ▁of ▁t aper , ▁whereas ▁pr ism ▁sh ar pen ers ▁have ▁a ▁fixed ▁sh ar pen ing ▁angle ▁and ▁produce ▁circular ▁symmetry . ▁ ▁While ▁most ▁linear ▁bla de ▁sh ar pen ers ▁are ▁simple ▁and ▁directly ▁hand ▁operated , ▁some ▁devices ▁in ▁the ▁past ▁were ▁c rank ▁operated , ▁using ▁mechan isms ▁to ▁convert ▁c rank ▁rotation ▁into ▁linear ▁motion . ▁ ▁C