Looking at a Dexter manual, that is exactly what they say....but they actually give a wrench length.
1. After placing the hub, bearings, washers, and spindle nut
back on the axle spindle in reverse order as detailed in the
previous section on hub removal, rotate the hub assembly
slowly while tightening the spindle nut to approximately 50
lbs.-ft. (12" wrench or pliers with full hand force.)
2. Then loosen the spindle nut to remove the torque. Do not
rotate the hub.
3. Finger tighten the spindle nut until just snug.
4. Back the spindle nut out slightly until the first castellation
lines up with the cotter key hole and insert the cotter pin (or
locking tang in the case of E-Z Lube™).
Castellation....so that is what they call the slots (holes) in the castle nut. Never knew that.