The infamous back-stab revealed! This is (was) a Leviton 15A 120V light-duty light switch.
Honestly, there's a surprising amount of contact area in there- there is a dimple sized for #14, and a large spring to hold it in place. The wire would have to be as straight as possible, though, or else it might only contact at 1 or 2 points instead of along the length. But installed properly, 3/8" of the wire will have contact along about 180° of circumference.
Edit: it's stamped MADE IN USA, btw
[This message has been edited by SteveFehr (edited 01-24-2007).]