I can see two ways of doing it: Make nibs the same width (M), but 'trim' the tines at the tip for making the B+ nibs. Doing so reduces the length of the nib slightly, but only one nib type has to be made.Make nibs the same length, but make different widths at the tip. Costlier to manufacture as each individual nib width has to be made in batches. Maybe I'm wrong, but sometimes I get the feeling some companies seem to follow the first method. Especially if you have a lot of EF/F nibs and need some B/BB nibs urgently...