Hi, I read a few posts regarding "How tight should the propeller nuts be?"
Some suggest that I refer to the specs of my drone. What I got is a iFlight Nazgul5 V2 240mm 5 Inch 6S Freestyle FPV Racing Drone. Not much specs there.

On my first flight, one screw came right off and lost in the grass ground. I should definetly tighten it better but I am not sure if I should tighten the nuts as much as possible, because I am afraid that would be damaging the motor. So what you guys thoughts on this?

Your nuts should have an anti slip material inside, so even if they get a bit loose they never go out of the screw. About tightness, just tight it until it bites the prop and you can't rotate it beneath the nut unless you make a lot of force to do so. Don't need to go bonkers and don't need any newton/meter gauge special tool.

Oh, and another thing if you tight pass the reasonable point, the prop will break way before you damage the bell so no worries on that.

(21-Apr-2021, 07:54 PM)Maiden Flight Wrote: Oh, and another thing if you tight pass the reasonable point, the prop will break way before you damage the bell so no worries on that.

Thanks for your reply.
Before I used a fastern purchased from Amazon, I hand tightened the nuts. I just realized that my propellers could spin independ of the motor, with means there is a huge space between the nut and the motor. Somehow with that terribly wrong setting, my quad took its first take-off OK before one nut went off the propeller spined away. I guess my 6s lipo was too powerful!
I will never make that mistake again.

The first time you tight a nut you feel the resistance from that lock ring and stop. That make a huge gap between the nut and the prop. Just go thru and tight it firmly until the prop is secure. You'll get the feel for it.

(21-Apr-2021, 10:43 PM)Maiden Flight Wrote: The first time you tight a nut you feel the resistance from that lock ring and stop. That make a huge gap between the nut and the prop. Just go thru and tight it firmly until the prop is secure. You'll get the feel for it.

I have tighten it with hand holding the motor as hard as I can.

But you are using a socket tool or something like that to help you right? If so, the only thing I could suspect is that your prop hub is not sufficient tall but that is odd.

https://www.getfpv.com/dal-prop-nut-tigh...-tool.html

1st time, using new M5 prop nut, its difficult.
Its comparable to using screwdriver to turn screw into wood.

If in doubt, apply strong force to prop. If it moves, tighten more.