The positioning bead (ball plunger and Spring plunger), also known as ball plunger or spring plunger. It is a kind of loading devices (SLDs) consisting of housing, spring, ball plunger or plunger. It is widely used on top of some medical device equipment, lubrication equipment, pneumatic tools and other products. Engineers often use it in molds, fixtures, assemblies and other work. With the help of a certain pressure of the spring to promote the movement of the ball, so that the smooth operation of the equipment.