The Oblique Penholder (Oblique Calligraphy Pen) is the standard tool (for right-handers) for Copperplate Script, Engrosser's Script, Spencerian Script, and Modern Calligraphy. These are slanted scripts with thin upstrokes and thicker downstrokes. To create the thicks and thins of these scripts with changes of pressure, your nib must be parallel to the slant of the letters. The oblique penholder makes this much easier to achieve for right-handed scribes. This is accomplished by an extension, called a flange, which holds the nib offset from the staff of the penholder. The flange can be of plastic (Speedball) or of metal, usually brass. Ideally the flange holds the nib at a shallow angle to the paper in order to reduce the chance of catches and splatters on upstrokes. All the metal-flange oblique penholders below do this. Only the Speedball Plastic Oblique Penholder does not.
Not all left-handers use the same penholders for these scripts. Some use straight penholders, others the standard oblique penholder or the left-hand oblique holder.