Summary: on the right hand side, and has a recessed 19mm head. The socket is the desirable way to go, as it allows you to use a torque wrench to properly torque the axle when reinstalling. I didn't want to spend the $35-40 to buy such a socket from MAC or SnapOn, as I'd so rarely use it, so I improvised. I got a 19mm lug bolt from a Honda automobile, and use it in conjunction
Image Dimensions: 262 x 353
Image originally found here.