A Double Knuckle Uppercut (sosum jireugi) is a Double Uppercut in which the striking surface is the knuckle of the middle finger. In other words, the fists are made with the center knuckles extented. The target is normally the opponent's jaw. The elbows should be held close to the body.
The Double Knuckle Uppercut appears, for instance, in the form Cheonkwon.