I'll toss this tool tip out, though it's been written elsewhere too. For my bike tools I have a separate set of small metric sockets - 10mm to 6mm - that I've modified. Many of the fasteners on derailleurs, brakes, clamps, etc have pretty thin heads (thinner than HW store or automotive nuts and bolts). To avoid damage to these thin hex's I've ground the ends of this set of sockets.

You'll see that a stock socket has a slight bevel at the inside end. Probably forged there to make it easier to fit the socket on a bolt head or nut. But with such thin heads on our stuff you can loose half of the grip area with such a bevel. I grind off that first 1/16" or so of each socket so the internal hex is flush with the end of the cylinder. When I use these they engage the whole nut or bolt head and apply much better force with less chance of camming off or rounding over the hex 'corners'.

Oh, I keep these special sockets together by stringing them onto an old spoke with the spoke nut on one end and a wine cork on the other. Don't loose one that way. Cheers.