Embodiments of an punch machine and a quick-change die assembly are shown and described. The die assembly may be quickly installed and removed from the punch machine, without bolting or unbolting of either machine housing or the die assembly itself. The die assembly is slid into the machine through a hole in the machine housing and into a position which mates part of the die assembly with the push-bar. A clamp, with a handle outside the machine, is then pivoted against the die assembly. The push-bar is adapted to be self-supporting without being bolted to the die assembly, keeping the push-bar in place without manual adjustment and alignment. The die assembly preferably includes a die, pin retainer, and punch pins, and preferably includes a flexible, pivotal, or hinged pin strap to secure the pins to the retainer. The preferred die assembly includes a positioning system that biases the pin retainer with its pin heads out from the die a proper distance for easy and unobstructed sliding into the machine housing and into a channel of the bar that drives the die assembly. The die assembly preferably includes a system for consistent referencing between various die assemblies, for reducing the instances in which the paper stop must be adjusted when a die assembly is changed.