In such a configuration one end of the follower is anchored (pivoting in place on a roller bearing), rather than having its fulcrum in the center like standard rocker arms.
The opposite end bears on the top of the valvestem, compressed by the force of the cam lobe acting on its upper surface.
Mass-produced car engines traditionally used a stamped steel construction for the rocker arms, due to the lower cost of production.
Rocker arms contribute to the reciprocating weight of the valvetrain, which can become problematic at higher engine speeds (RPM).
Diesel truck engines often use rocker arms made from cast iron (usually ductile), or forged carbon steel.