After the hi-lo push-pull in naihanchi comes another distinctive feature of this kata - the hammerfist. There are three repetitions of it - one facing forward with weight stable on both feet, and two facing the corners and dropping weight onto alternate legs.
The hammer is absolutely my favorite closed-handed technique. I can hit far, far harder with a hammer than with any other fist-technique. When we used to do board-breaking techniques in karate, our instructors made the beginner breakers always start with a hammer because it's a safer way to build confidence. I don't know of many techniques that I'd brag this way about, but if I get scared and pull out the hammer, you're not gonna enjoy being the anvil.
In naihanchi, the targets are typically neck and jawline and temporal zones, but this thing can also be extrapolated to elbows and kidneys and collarbones without much stretching of the mind. perhaps my favorite application of the forward hammer is against a chest grab/push - lay your free arm across his arms to hold his hand(s) to you, twist to jerk him off-balance to a corner, then drop a hammer into the angle of his jawbone with the impact happening slightly toward yourself. Likely consequences are severe.
Then again, with a hammer you can hit so infernally hard without hurting yourself, that even without precise targeting, you can get great results, as Bud Spencer demonstrates several times in this following clip...