I'm looking to upgrade the rollers. After googling a while I see in-line roller skate wheels are one option, but I'm not quite clear what I need: in-line wheels, bearings, and M6/M5 bolts depending if attaching to the frame or rack. Do I need anything else...washers, axles...or is that it? Do they need to be in-line wheels, or will quad skate wheels work also? Or other alternatives to the stock cones/rollers on the back? - feel free to post a pic of what you're using.