CAM bolts

With no other information or details to go on, cam bolts are used to make very precise alignment adjustments. Sometimes the manufacturer leaves those off to save a few dollars, then they expect the owner to pay for them later. That isn't a problem when the car is new on the assembly line because the alignment will be close enough. As the car ages and the springs sag, the geometry of the suspension system changes. Metal fatigue also plays a role in the need for periodic alignments. Some alignment specialists will say if a non-adjustable alignment angle was good enough for the engineers at Ford, it's good enough for them too, and they let you go with a less-than-perfect alignment. You might have a slight pull to one side or accelerated tire wear. Conscientious alignment mechanics who have your best interest at heart will want to replace the original bolts with cam bolts so the angles can be set more precisely to provide the best handling and tire wear. Once those cam bolts are installed, they stay there for the life of the car. You only buy them once for each control arm, but you don't have to buy all of them at the same time. The typical time to buy them is when that arm is replaced or when a certain angle needs to be adjusted.

Be aware too that no two control arms are ever exactly the same. That's why there needs to be some adjustability when parts are replaced.

Just saw your second post. When older rear-wheel-drive cars used solid rear axle housings, nothing in the back could be adjusted. We still performed four-wheel- alignments because the computer looked at the direction the rear wheels were steering, then had us set the front wheels to match them to insure the steering wheel would be straight. It was common for the rear axle to be skewed a little causing the rear to "dog-track" off to one side a little, but much too little to be noticeable. With that solid rear axle housing, the rear wheels had to be standing perfectly straight up and down all the time.

Most cars today have independent rear suspension and both rear wheels can be adjusted for the direction they're steering and to be tipped in or out a little on top. Tipping them in aids in high-speed cornering, but at the expense of tire wear. The alignment specifications also take into account how the geometric relationship between all the parts in the suspension system interact and change as you add more people in the back seat. That wasn't an issue with solid rear axles, but now, independent rear suspension is a compromise that can improve ride quality, but it greatly accelerates tire wear.

With the new cam bolts in the rear, besides setting the alignment angles to specs, the mechanic can modify the settings to improve tire wear when he knows how the car is normally loaded. For example, if a traveling salesman always has a few hundred pounds of samples in the trunk, the mechanic is going to want a heavy load in the car when he is performing the alignment. If he knows the car is only driven by an elderly couple, he is going to want to temporarily remove the 50 pound bag of dog food in the trunk while he sets the alignment, since that is only in the car one day out of the month.