NEIEP Mechanics Practice Exam

The head of the jack is designed as the striking surface for the plunger stop ring. In hydraulic and mechanical jacks, the head is the uppermost part that interfaces with the load being lifted or supported. When the plunger is activated, it moves upwards, and when it reaches its maximum extension, the stop ring comes into contact with the head. This contact serves to limit the upward travel of the plunger and helps ensure the jack operates within safe parameters, protecting both the equipment and the load being lifted.

The shaft, while integral to the lifting mechanism, primarily provides the pathway through which the plunger moves rather than acting as a striking surface. The base serves as a stable support platform for the entire jack structure and does not come into contact with the plunger stop ring. The plunger itself is the part that moves, but it does not serve as a contact surface for the stop ring; instead, it interacts with the head at maximum extension. Thus, the head is the correct answer as it plays a crucial role in the operational safety and functionality of the jack.