How can I remove the small slitted nuts to open an old rear hub? This is an old back hub that has back-pedal break, and two internal gears. As pictured it has two slitted nuts that lock the hub.

Which tool should I use to remove these nuts without damaging them?

Is there some way of removing them without a special tool?
With an angle grinder and a flat file you can easily make a tool for this purpose from flat iron (preferably hardened):



If you use hardened flat iron, make sure to spray or dip it in water regularly too not lose the tempering when grinding. The small tip that fits into the slit of the nut needs to be finished with the flat file since the angle grinder doesn't reach to make it the right angle.