Jobber = Standard length.
Mechanic = shorter than jobber.
Screw Machine = shorter than Mechanic.
Aircraft = longer than jobber (not really useful for pen making).
If you bought a set of drills without knowing any of the above you most likely bought jobber. So that's probably what you already have.
That said, if you need longer drill bits, you can buy whatever length bits you need. Buy the length you need and don't worry what they are called. If you buy the length you need, you know you are getting what you need rather than relying on a generic size classficiation and hoping it works.
Ed