This fist can be tightened in two ways. All fingers except the middle finger can be closed as in tsuki, with the tips of the ring and index fingers touching so that the middle finger does not slip into the palm.
In the alternative, the indexﬁnger is extended toward the wrist. At the same time, the thumb presses the other fingers together.
The Nakadaka ippon ken hits small vital points with the second knuckle of the Mittelﬁnger, which cannot be reached with other techniques due to the larger hitﬂächen.
This technique can also be used for defending (at the same time it is intended as an attack on the attacking hand - an example of this is the kata Chinte).
Here you will find all information about the techniques in the video