What is the difference between self-aligning and non self-aligning rocker arms? What does "self-aligning" mean?

 

Self aligning rockers have "nubs" on the valve stem side of the rocker arm that straddle the valve stem and keep it aligned. You cannot use guide plates in these applications because the pushrod will bind.

Non self aligning rockers or "regular" rockers use guide plates for larger lifts.