Rollerball pens combine the elegance of a fountain pen with the ease of a ball point.  They differ from a ball boint in that they use a water-based ink which flows onto the paper smoothly without the drag of a ball point, giving a feel similar to a fountain pen.  The ink takes a split second longer than the petroleum based ball point ink to dry, allowing it to soak into the paper a bit more.  This "wet" ink deposition gives the rollerball an unusually smooth feel.  After trying one of these, you'll want to throw rocks at any disposable ballpoint you've ever used.

Pens with removeable caps (fountain and rollerball types, which use water-based ink) are made in two types: posting and non-posting.  Posting styles are designed so that the cap is unscrewed from the tip and screwed onto the back of the pen when in use.  In non-posting pens, the cap is intended to be stood on your desk to impress your clients as you write.  Some people prefer the balance of the one over the other.

There is an excellent article in Wikipedia on the history of these writing instruments.  

These pens use a standard Schmidt® style refill.    The pen measures approximately 5" long, the cap is approximately 5/8 diameter, the body approximately 9/16" diameter.  Care and use instructions are included with each pen.

 non-posting, 10k gold plating with black enamel accents, beechwood body   

                                                                                    #57   .........................$60