So here's how I "think" it's intended to be fit:
The propellor fits loosely over the threaded part of the motor shaft. Once it's slid all the way on over the non-threaded part at the base of the motor, it's snug with no apparent wobble or play. The only supplied collar that has a big enough opening that it slides snugly over the threads slightly insets into the front of the prop and there's still enough thread protruding that the nylon insert of the nut engages and keeps it from unscrewing easily.
I tried putting the same size collar on first before the prop, and it only fits over the threads and can't be pushed further onto the non-threaded part. With it configured this way, there is not enough threads exposed on the front-end to get to the nylon insert of the nut and engage.
What do y'all think? Again, thanks for the help!