A stamped steel cog has tougher threads than a cheap aluminum hub.

Sad but true.


Besides, the motion of the hub (forward) against a (relatively) stationary cog will only have a tendency to spin off (unthread). The danger zone is when you stand up to accelerate from a stop and spin the cog into the hub. It can't follow the threads since it's bottommed out next to the hub flange, and the rotational force (help me out physics guy) on the cog runs it's (stronger) threads across the (weaker) threads of the hub.