[martin417]

The mystery is solved. We didn't use self locking nuts because the ones we had were too tall to fit. We had a student put the wheels together and he use too much blue loctite (blue seems to be worse on polycarb than red) anyway, every wheel had cracks radiating from the nut locations.

Note to all: NEVER USE LOCTITE NEAR POLYCARB!!!!

PLACTION WHEELS ARE POLYCARB!