Other discussions of this topic - such as in FiberglassRV - have mentioned the verification washer included in the special U-Haul ball nut system
: the washer (or "Exclusive clamp indicating fastener") squishes out from between the nut and washer when the nut is sufficiently tightened, a reminder that proper tightening is important, and without it one might be concerned about the nut loosening.
The same system from U-Haul includes a cotter pin, but it also uses a "Hardened flat washer instead of a lock washer". Properly tightening, using a lock washer (or locking nut) and
wiring or pinning just seems excessive to me. The more complex an operation, the more likely an important step will be missed or done improperly - a reason why aftermarket "safety" gadgets generally seem like bad ideas to me.
I suspect that all this attention to keeping the ball nut on at U-Haul stems from three sources:
- U-Haul staff are supposed to assist customers with hook-up, but the clerk at the convenience store / liquor outlet / U-Haul franchise is neither qualified nor inclined to ensure that anything is done, let alone done correctly;
- many U-Haul customers are first-timers who have no clue what they are doing; and,
- the idiotic "fits everything from 1-7/8 inch to 2-1/8 inch" handwheel coupler favoured by U-Haul has no correct setting (because it doesn't fit any particular ball size) and thus may be cranked down tight by enthusiastic users, causing the trailer to apply turning torque to the ball in corners, perhaps loosening the ball.
None of those factors apply to me, so I don't feel the need for the cotter pin (or safety wire). Everyone's situation is a little different.
I note that even U-Haul also sells normal balls, with a split washer and no cotter pin (or safety wire hole). To their credit, it looks like all of their balls have wrench flats at the base of the ball itself... handy to get the tightening started, or sometimes to hold the ball when breaking the nut loose.
If I wanted a safety backup, I would rather buy the U-Haul fancy ball system than drill the nut and shank of a stock ball.