The technical details of rod ends make a whole subject unto themselves. Briefly, some rod ends use a hardened race between the body and the ball as shown in the rod end on the left. Others, such as the one on the right use a dense synthetic material between the ball and body. The material is self-lubricating and has tight tolerances to keep debris and contamination out of the bearing surfaces. These tend to work best for off-road steering applications. For reasonable rod end sizes, it’s not very common to see outright rod end break failure on a quality part, but more likely looseness grows over time. Once a ball begins to get loose in its race, subsequent loading will bang it back and forth, accelerating the wear and play between the two parts.