Needle Cap used for all flat needles, 3 flat, 4 flat and 6 flat Not enough air causes a "vacuum" effect and sucks up pigment. Too much air can force pigment down too hard and will splatter, and less pigment gets to the skin. Less pigment in the skin will cause the color to fade. Merlin caps regulate the airflow for an even amount of pigment and better result. When we say less touch-ups, we mean it, because we did it right the first time!