[Mike Kelly]

Adding to what Lang wrote . Some components are case hardened, meaning the outer thin layer is hardened and the centre remains in a softer state which is ideal for bits like gears and king pins , the centre has a bit of ' give ' while the surface is hard enough to withstand wear. They use special steel for case hardening the EN series. I was looking into machining some Morris king pins out of EN 26 and getting them treated then ground to size. You can run a file over the part to get a rough idea of how hard it is .