Rocker arm bearings are mainly used in the cam mechanism of the cylinder head of automobile / motorcycle engines, and assume the normal opening and closing functions of the valves. They play an important role in the intake and exhaust of fuel and combustion gases in the engine. When the engine is running, the cam will continue to rotate. In the past, when slider rocker arm was used, the force is transmitted from the cam to the rocker arm, which is called "sliding contact". Now "rolling contact" with less friction is realized by using a full complement needle roller arm or roller rocker arm. The bearing structure is divided into two categories: one is needle roller bearings, which are composed of outer roller, rolling element (needle), and shaft pin; the other is roller sliding bearings, which are composed of outer roller, roller bushing, and shaft pin or composed of the outer roller and the shaft pin. Due to the limited space of the engine cylinder head, the bearing specifications and sizes are basically similar. The inscribed circle of needle roller bearings is generally within 7-16 mm, and the outer diameter is generally between 17-30 mm. The size of sliding bearing is slightly larger than needle roller type, with outer diameter ranging from 35 to 45mm.