Take a look at these Snap-on and Metrinch sockets (on the right). They are designed to work so they do not touch the corners at all. The corners are weak. The sides of the bolt are strong. So they won't round over the bolt head, and will work on bolts that were previously rounded off.

http://forums.pelicanparts.com/uploa...1594650643.jpg

And then you might also try Home Depot. They have sockets that are uniquely designed to work with many types of bolts, including German triple-square.

http://forums.pelicanparts.com/uploa...1594650768.jpg