The mid-barrel of the fountain pen features a captive collar that is rotated to operate the filling mechanism. The interior wall of this collar is machined with two symmetrical, opposing internal cam ramps spanning its full internal width and circumference.
Inside the barrel are two opposing pressure bars, each fitted with a small follower tab that projects outward into the collar. As the collar is rotated, the tabs track up the escalating profiles of the dual cams, forcing the pressure bars inward to gradually deflate the rubber ink sac.
Each cam profile terminates at exactly 180 degrees in an abrupt drop-off. Upon reaching this cliff, the independent spring tension of the pressure bars causes the follower tabs to instantly snap back outward against the inner walls of the barrel. This produces a distinct, tactile “click” and allows the ink sac to fully expand and draw ink. The mechanism allows for continuous, unidirectional rotation, cycling through a full compression and release every half-turn. After filling, an integrated collar lock is engaged.
Mechanically, it acts like a mid-barrel version of terminal cam-style mechanisms (such as the Turnstile and Matador fillers). Additional interest comes from the locking notch and the two distinct design variants used to engage or disengage the tabs from the collar, as described in detail in the 2008 Clickit article.