I've got a late 80s specialized hardrock and I am curious about these rear dropouts. What is the purpose of the hole in addition to the regular slot dropout? Can I mount the wheel through here? I am curious because it could provide more clearance for some cushier tires.

I am also curious about the rear hub. It has a nut on each side that locks the wheel into the dropouts instead of a quick release. At first I thought I could just remove these nuts and the axle and replace it with a quick release. But the axle seems to be part of the hub. Is it possible to put a quick release on this hub?

Thanks all