Pictures of acceptable rounded model aircraft type safety nuts and spinners are attached below. You do not have the exact units pictured, but any spinner or model aircraft safety nut your team uses must closely resemble these examples.
Aero Design requires this type of spinner or model aircraft type safety nut for safety reasons. If an aircraft goes out of control and hits a person, this requirement helps lessen any chance of injury by covering the threads of the prop shaft and making the front of the aircraft have a more blunt point. A spinning exposed threaded prop shaft can cause a more serious injury than one covered by the required spinner or model aircraft type safety nut.
A locking type nut that locks with a fiber or plastic insert is not considered a model aircraft safety nut.
Using two regular nuts or fiber locking nuts together is not a substitution for a model aircraft type safety nut.
Note that a model aircraft type safety nut complete covers the end of the prop shaft and is smooth and blunt on the front.