How to secure a square shape shaft end without a square cut on the mating component

When we want to prevent the rotation of a shaft we use various methods (pinned, screwed, friction, etc.). One method is to use a shaft with a square shaped end (across flats) and an identical square slot feature on the mating part. Manufacturing a square end on a shaft is easy, but the corresponding square cut needs special machinery which is costly or at worst not available.

An easy way to apply such a connection is with the aid of a simple milling machine as described below:

Instead of machining a square cut, one can make an oblong slot and a hole with a square end cutter. We machine the oblong slot with a width equal to shaft across flats and a hole equal to shaft diameter on the opposite surface.

The mating is secured against rotation and axial movement (one way by default, both ways if we provide an extra fastening method).