On the left is a twisting punch viewed from the front. Note that the hand starts off open and is closed on its way to the target to create greater initial speed. Also note how the non-punching left hand maintains a constant guard. Initially the palm defends the right side but in 5A it becomes mainly a left side defence as the extended punching arm moves into a position where it can cover the right side.
The right side of the scan shows a punch from the side, but in this instance the non-twisting variant. Note that in photo 6A the arm is not fully straightened. In fact it can be seen that forearm, hand and the proximal bone of the finger form a smooth curve to allow an uninterrupted flow of force.
Image scanned from “Phoenix Eye Fist” by Cheong Cheng Leong and Don F. Draeger.