COMP Cams® steel rocker arms are all constructed from 8620 or 8650 chromemoly steel, which is a higher grade material that makes them extremely durable and tough. The material keeps them from flexing, and they have large trunions and more needle bearings, which allow the load to be more evenly spread and the rocker to last longer. Steel can thus be run in harsh environments without fatigue issues. Steel will actually only become weaker to a certain point and then stop and retain nearly half of its original strength throughout its life. And some COMP® steel rockers are even lighter than some aluminum because COMP® has reduced mass in low stress areas.