Seriyūtō uchi is often called a wrist bone strike or an ox jaw strike, though we typically default to the Japanese name, since there’s no straightforward English equivalent. Seriyūtō uchi is a modified version of hassō-shutō uchi which impacts the target with the end of the shutō, where the hand meets the wrist. This condenses the force of the strike down to a single point, for a more penetrating attack. This is most commonly used in place of a straight-down “12-to-6” hassō-shutō uchi.
To perform a seriyūtō uchi, hold your hand above the target, with your fingers pointing down and away from you. Then, drop your wrist down and snap your fingers upward. This drop does not need to be large, and a skilled karateka can use seriyūtō uchi to break a board from 6” (15 cm) away. The hand’s “crack the whip” motion imparts additional snap to the technique, augmenting its power.
[Seriyūtō uchi fast and slow, from the front and side several times.]