Which side of either a plain or self-locking bearing nut faces the bearing?

The correct answer is that the side with the big chamfer faces the bearing. In bearing assemblies, particularly with nuts, the design often features a chamfer which serves multiple purposes. First, when the chamfered side is oriented towards the bearing, it helps guide the bearing into the nut smoothly, reducing the likelihood of damage to either component during installation. Additionally, this orientation ensures that there is optimal load distribution across the bearing and nut interface, which is crucial for the longevity and efficient operation of the system.

The flat side, while it may appear functional, does not provide the same guiding benefits as the chamfered side. The jagged edge side, if present, could create undesirable wear or stress concentrations, while the threaded side is meant for engagement with the bolt or screw and does not have an appropriate design to interface with the bearing. Thus, the chamfered side is specifically designed to face the bearing for the best performance.