Products     Metric Grades and Sizes   Cobalt % Grain Size For 7x4 through 25x20     GC-106 6 Fine GC-206 6 Medium GC-209 9 Medium GC-313 13 Medium For 30x24 through 45x25 GC-313 13 Medium GC-315 15 Medium GC-618 18 Medium/Coarse GC-970 17½ Coarse All pressed nibs/pellets meet or exceed the industry's highest precision standards: +/-.03mm (0.2mm < I.D. < 2.5mm) +/-.04mm (2.5mm < I.D. < 5.0mm) +/-.06mm (5.0mm < I.D.)