What is the difference between ball point and roller point pens? To me, I don’t see much of a difference beyond price. What puts the “roller” in roller point, and what makes it worth the extra cost?
Ball-point pen ink is an oil-based ink in the form of a paste, which must be melted by the action of the rolling ball at the tip. Roller ball ink is liquid, similar to fountain pen ink. This is why ball pen refills write longer than roller ball refills, but are not as smooth. I’m not sure whether it’s the restocking frequency, the engineering of the pen, or the complexity of the ink that’s responsible for the high cost of rolling ball pens.
According to this site (http://www.theinkflow.com/f_a_q_'s.htm) one difference is in the ink.
Ballpoint pens use a thicker, paste-like ink, while rollerpoints use liquid ink.
Dunno if there are any real mechanical differences between them although comparing a Bic and a Uniball sitting on my desk I’d say that the Uniball (rollerpoint) has a smaller ball than the Bic, probably because of the difference in inks.