I mean is it me or haven't I seen both in use on various bikes? An axle seems ideal if you've got space for a nut on each side of the mounting hole. I see how you could lock in an axle position as to the frame itself, on either side, and also be able to control for just a hair of slack for the wheel hub to spin without the same left-to-right thrust pressure that a bolt necessarily creates. I believe my bonanza has axles, but otherwise I've gotten away with bolts (12mm), from the hardware store, and I've just assembled carefully, while caring a lot about not over tightening and stressing the radial bearings. Call me naive, call me cheap, or just lazy. But now I'm asking the all-powerful minds here for your opinions. In part because I've been restoring for fun, not accuracy, but also because I haven't exactly come across a lot of axle dealers on line. What's your go to?