The 66 Septagonal body has 7 facets or flats milled into each cap and barrel, which also serves as a roll stop feature. 

As the company writes;

♦ Features special block threads at the end of the grip section. These smoother threads lie out of the way of your fingers. Placing the threads at this spot limits the amount of air within the cap chamber, thereby helping to eliminate dry out. The design of the block threads also releases the air when you unscrew so as to not create a suction effect on the ink. 

♦ Each pen can be filled via long or short international cartridge, by converter, or via eye dropper. They recommend a little silicone grease on the threads if you use as an eye dropper. Barrel holds approximately 3.5ml of ink.

♦ Lifetime Warranty

♦ Made in USA 

♦ Zippered pen pouch is included. 

♦ Dimensions:

capped length = 6.30"

nib tip to barrel end = 6.10"

cap posted full length = 6.85"

barrel diameter near cap = .55" 

grip section smallest diameter = .42"