In Japan, black and gray ink pens are used frequently during the holidays for elegant writing on cards in announcements. Many American artists and crafters have fallen in love with such pens because it combines often used colors for artwork. The pen is double-sided with a black ink felt tip marker on one side and a gray ink marker on the other side.
However, a second reason that this marker is so popular is because of its balanced and light weight that makes it perfect for pen spinners. It is the pen for the popular Dr. KT mod.