As we saw in the Karate post, the open hand of China has not widely survived in most Okinawan or Japanese (thus the rest of the world), martial arts Kata. It seems as if the fist has won that round.
The use of the fist could have been a development from the prior arts for its simplicity in training, conditioning and application (the clenched fist being a natural tendency in men during high stress). Or it could have been that the indigenous methods already made heavier use from the hard work in that land; such as fishing or farming and the "clasped hand" on rope or tool. In any case it is imbedded firmly in all but a few styles in modern times. So let's further explore this in regard to the myriad of weapons on the fist as opposed to just the fist.
First we must notice the structure of the fist, as to its possible weaponry. We have wide areas that can be used as bludgeons (typical in most modern adaptations of the style). These include a full frontal fist, back fist, or hammer fist... All requiring heavy force, velocity and distance to employ adequately. These three areas of a closed fist yield a very inefficient weapons, especially used against larger opponents. And as they require distance, power and velocity, they also are more susceptible to injury of self on impact.
Another set of weapons that can be utilized from a closed fisted hand are the smaller protruding bone structure called knuckles. These smaller extended bones can produce a deeper penetration between the protective structures of the human anatomy. They can attack the weaker physiological structures between bone, muscle and tendon causing greater pain or dysfunction with less force, velocity and distance. These type of attacks not only increase efficiency they also increase the angles of use due to the larger number of weapons as opposed to just the broad surfaces. They can be delivered with equal affect in almost all angles including back to front... This can continue their use even in very tight combative entanglements.
There are many kata that use the Fist but none as concentrated on the multiple angles of the knuckles as Nai Han Chi. This is due to the most prolific use of fist (knuckles), positions, rotations, transitions and angles as well as attacking surfaces. If you concentrate your thoughts on the targets, then access them spontaneously and naturally as presented with the most available knuckle that will access it correctly, then these ideas instead of technique, will create many more spontaneous applications. This will serve in giving you a much more diverse and natural (your inherent tendencies) combative potential.
All the positional changes of the fist in the actions of the arms also contain myriads of fist rotations or actions. This allows the practitioner a vast number of attack possibilities as well as actions. To realize this gain a standing clench position on your opponent with your hands around their neck (signifying the opening action of the Kata). Then as you are in that position work any knuckles on any target you know. This initial posture and applicational them will help you realize several available knuckles and targets with a back to front trajectory.
Using this formula you can then decode the myriads of possibilities from other starting positions to access more targets with angled knuckle work. Stick with the knuckles to fully gain the ideology and potentials. Once you have exhausted your creative applicational potentials, move to the second section of this Tri-sectional Kata.
Another stage in this investigative combat regime can lay in the actually closing of the hand as you clench the fist. Using the finger or thumb tips now for the weapons we can affectively work with more seizing and tearing type actions. Once the hand (fingers) are placed in position, the rotations can then apply a rotational torque to the attacked target or structure to stretch, tear or compress to achieve control. We must never loose sight of both yin or yang qualities in each thing or action.