Rod
Ends 
Canberra Hot Rod Association (CHRA)
Four Bars, Rod Ends and Bushes
Have you ever notice that a lot of 4 bar setups have loose jam nuts?
4 bars weren't designed to twist. They're only good at keeping axles aligned with the frame in a vertical plane. Lift one end of the axle and not the other and all four of the links want to twist. It's like trying to twist a cardboard box. It doesn't want to twist because it wasn't designed to twist. When the 4 bar assembly twists, the bars themselves twist. This twisting tends to want to loosen one or both jam nuts on the 4 bar.
If you drive a lot on back country roads or in and out of a lot of parking lots or driveways with pronounced grade changes, you're probably driving around with a loose jam nut or two and you don't even know it. So, what's the big deal, you ask? Well, all that driving you're doing with the loose jam nut is wearing out the threads in the link. Why? Because the end is constantly pivoting in the bar and wearing out the un-lubricated threads. Instead of twisting the urethane bushing, you're running the thread in and out. Every time you take the car out for a cruise, finger the nuts and see if they've loosened up. It's cheap insurance.
If you want to minimise the problem, switch to a hairpin style of wishbone with a tie rod end (pivot, or rod-end) or go back to the old standby split or stock wishbones. Urethane bushings don't flex enough and the stress is felt at the jam nut, even on a hairpin wishbone.
All but the stock (un split) wishbones will "load" the frame and suspension whenever the front and rear axles are not parallel or when the vehicle tries to tilt as a result of cornering. The whole reason for splitting the wishbones in the first place was to improve cornering stability by loading the suspension as the vehicle tried to roll. With the split stock wishbone/tie rod combo used for decades at least there aren't any jam nuts to loosen up. Same goes for the hairpin wishbone if it's got a tie rod end for a frame anchor.
Remember, too, that urethane bushings must be squeezed tightly between a pair of tabs. Urethane bushings are not designed to move on a shaft or in a tube like an oilite bushing or a bearing. They're a substitute for a rubber bushing and should be clamped accordingly. They're supposed to twist, not slide. When they slide they wear out VERY quickly.
Heims vs Rod Ends
So, is the answer a spherical rod end (Heim) so it will swivel
instead of the rod twisting on the threads? No! Heims, or Spherical Rod
Ends, weren't designed to be run in the hostile environment you normally
find on our motorways. They are used on a lot of race cars, but they get
tossed after the race is over anyway. If you run these on the street, they
tend to wear quickly because they get full of dirt and grit. That's one of
the reasons NSRA requires a larger-than-the-ball washer. It's to stop the
worn out joint from popping off.
Skip and his NSRA Safety Inspectors inspected a Chevy pickup one year that had spherical rod ends everywhere in the suspension. No washers, just the rod ends. The owner insisted they were good because they were oversize. (He was right there. They WERE oversize. They were huge). I had him lock up the parking brake and we rocked the truck back and forth. You could hear the clunk clear across the pavilion. Needless to say, we didn't give him an inspection sticker. The rear was about to fall out. It didn't look too bad just standing there but the pinion was moving up and down about 2-1/2 inches just rocking the truck back and forth.
Even though we pointed out the excessive slop in his
"good-because-they-were-oversized" joints, he still called us jerks for
refusing to pass his truck. Spherical rod ends weren't meant for over the
road use. The environment is simply too hostile for them to
last.