A mechanical timer is a device that uses mechanical devices to achieve timing functions. It usually consists of the following main parts:

Spring: The mechanical timer has a spring inside to store energy. When the spring is tightened, it stores energy and releases it when the timer starts working.

Gear system: The mechanical timer has a set of gears inside it, which are used to transmit energy and control the passage of time. These gears typically rotate in specific proportions and speeds to ensure the accuracy of the timer.

Pointer: A mechanical timer has one or more pointers inside to indicate the passage of time. These pointers are usually connected to the gear system and move over time.

Switch: There is a switch inside the mechanical timer that controls the start and stop of the timer. When the switch is turned on, the timer starts working, and when the switch is turned off, the timer stops working.

Adjustment device: Mechanical timers usually have some adjustment devices inside to adjust the accuracy and time interval of the timer. These adjustment devices can be knobs, buttons, or other forms of control devices.

Overall, the internal structure of a mechanical timer is composed of springs, gear systems, pointers, switches, and adjustment devices. These components work together to achieve timing function through mechanical principles.