Drill

In case you didn't see the comments in reply to my previous post, here is the answer to "how can a mains electric drill with a metal gearbox casing get away with a plastic earth pin on it's plug ?"

The answer is "double insulation". The theory is that even in the event of breakdown, nothing live is able to touch the casing. It's slightly cheaper to make this way, hence economies of scale kick in.

Just to complete the story, double insulation should be notified on the casing of the device with a concentric pare of squares :

Thanks for your input J&B and Chris.