hex nut problems

hi every body
i have an all ali brushless emaxx which is just about built the way i want it,
but i have one problem the hex nuts that fit into the wheels keep spinning and either stripping the wheel or rounding off the hex nut itself. will changing
them to metal ones cure this or should i just bond a set of plastic hex's to the inside of the wheels, hopefully someone else has seen this before and will have an answer , thanks.



my specs
Lehner LMT 1950/8 Brushless motor
MGM 24/160 Brushless ESC
KoolFlightsystems UBEC
18 cell ib4200 batteries
strobe slipper , metal cvd's etc