Originally Posted by
Troul
dremel it to take the next size up allen key/hex.
Ooo, that's a good idea, if there is a small enough diameter cylindrical stone. The corners are not a problem, they have found that sockets with the corners relieved with a radius, are actually less likely to strip; it's called Flank Drive, invented by Snap-On in the middle 1960s in response to the US military having problems with rounding off high-strength high-torque fastener heads when removing.