The TWSBI Diamond 580 is now available in their most popular IRIS color! This pen has  transparent body and unique rainbow metal accents, no two are the same! Pre-orders begin July 13th and will ship July 15th! This pen uses a classic fountain pen with a piston ink-filling system. By fusing the traditional mechanisms of the fountain pen with a modern industrial design, TWSBI has created an eye-catching fountain pen that is simultaneously appreciative of the past and relevant in the present. This pen comes with a benchmark ink-filling mechanism and has all detachable parts. TWSBI felt that it was important to allow the user to disassemble and reassemble the pen and completely experience the traditional aspects of owning and using a fountain pen.

Note: This pen does not come with a bottle of ink and does require one to be used. 

A quick no brainer guide in choosing nib sizes in an overly complicated fountain pen world:

If you write small, go with an EF
For the normal writer, F is the most popular
If you tend to lean on a bigger font, M will be perfect
B is for statements!! Sign a check in B, write a header in B, do some coloring/shading in B
Stub nibs are italic in writing style (have a special card or invitation to write?)