Posca 5M White
To start using the marker, shake it with the cap on so that the ball inside rattles. Then uncap the pen, place the tip on a piece of scratch paper, and press down so that the tip is pushed back into the body of the pen. Press the tip down several times until the ink begins to flow.
This pen has a medium tip, which produces a line between 1.8 mm and 2.5 mm wide, depending on writing pressure.