It's just a metal/plastic sandwich.
It's similar, but a bit stronger, than the zefal's I've got on my road
bike.
The Zefal's are very brittle, and mine are held together by a couple
mending plates and screws. Drilling is not a problem.
http://static.flickr.com/39/76033586_dd0763ba92_o.jpg
A regular wood bit works fine.