A rear axle hex nut is very common on most bikes equipped with or without a multi-speed shifter or Derailleur.  It can be removed with a common wrench or socket. The rear axle nut must have 3/8" thread to fit FATWHEELS Small and Large kits.

The quick disconnect lever allows the removal of rear-wheel without the use of tools.  Quick disconnect rear wheels do not use a hex nut to fasten the rear wheel to the bike.

The Nexus shifter comes in both 3 and 7 speeds.  It is not to be confused with a Derailleur.  The Nexus shifter shifts through the center of the rear axle via a cable like a traditional multi-speed bike.