A press fit ball plunger is a type of fastener used to secure two or more pieces of material together. It consists of a cylindrical body with a threaded end that is inserted into a hole in one of the pieces of material, and a ball at the other end that rests against the other piece of material. The ball is held in place by a spring, and when the plunger is pushed down, the ball is forced into the hole, creating a tight fit. Press fit ball plungers are commonly used in applications where a high degree of precision is required, such as in electronic components and medical devices.