Those self-locking (or prevailing torque) nuts are always identifiable with one small trick. Spin the nut all the way on by hand only. Can you? If you can, they are not self-locking. If you can’t they are, assuming there isn’t corrosion getting in the way.
Edit. The serrated f l a n g e nuts CAN be spun on by hand! They are a good choice in some applications
Nyloc nuts can melt in high heat locations. Cotter pins are a PIA in the assembly plants. Loctite (or other brands) can be applied dry to bolts so that once they are used, the Loctite is activated…but that is expensive. Metal self-locking nuts are the preferred solution…cheap and easy.
Just my 2 cents. As Nevada etc. showed locking nuts generally have that depression stamped in them. Once used they lose their locking. Caoability. Then there are the nyloc nuts, and lock washers etc. I would rather re-use an original nut using loc tite where I knew the grade of th3 nut, rather than some other after market nut.
When in doubt, on anything I might do, I just go with grade 8. Granted there are areas where a higher grade might be required, but I won’t be working on that part.
Right or wrong, I have always (unless damaged or lost) reused those (and most all) steering and suspension hardware (nuts/bolts)…
I think the manufactures say to replace some parts more as a CYA then anything else…
IF the nut states on it One Time Use or Do Not Re-Use or whatever, THEN I replace it…
I guess you need to evaluate your time verses your expense… The first time “re-used” the “Do-Not-Reuse” nuts were on my '83 Mercury Lynx when I replaced the Valve Stem Oil Seals. I had to remove or loosen the Rocker Arm Hold-Down Bolts and I reused the same nuts not knowing that they were “one-use-nuts”… It did not take long before those rocker arms started loosening and rattling like an old Singer sewing machine… But I never made that mistake again…
Remember the intake belly pan leaks on the 5.2/5.9? When replacing that gasket we were told to replace the bolts. Not because they were a TTY or one-time fastener, but because techs couldn’t be trusted to clean threads and apply fresh Loctite.
Ford Transit Vans brake rotor-to-hub bolts same thing. Service manual says replace after each use, yet the Ford dealer doesn’t stock those bolts.
These may be what are called distorted thread locking nuts. If so, they should have an indent on one of the hex flats. They are not meant to be reused.
Just be aware, harder is not always better. In fact, under some conditions, it can be very hazardous choice to make. Case in point- a buddy lost the hardware part that suspends his plow. He went and bought a grade 8 bolt to replace it. Harder is better right? Nope. That shock load requires a softer metal to absorb the shock (shear force) encountered with the plow bouncing going down the road. The consequence was the harder bolt shearing off and the plow slamming onto the ground at freeway speed. Fortunately, other than needing a change of underwear, nothing worse happened but it highlights the need to understand the forces and choose the correct hardware for the task. When in doubt, use what was specified. It would be better to re-apply locking compound to the existing nuts than to second guess the original design choice…
