Capitol's 350AC is a piston fill fountain pen with a difference!
-Twist knob locks in place so there's no chance of emptying the ink fill inadvertently. Simply line up the arrows, pull up the knob, fill, and snap the knob back into its locking position. Your fill of ink is safe from the piston being twisted downwards even with the cap posted!
-Gasket above the grip section helps create an airtight seal to keep ink from drying when 
 capped.
-Schmidt steel nib in extra fine, fine or medium point is mated to a proper feed for smooth,      consistent ink flow.