A hinge pin is a cylindrical rod that serves as the pivot point for a hinge, allowing two objects to rotate relative to each other. It is commonly used in doors, gates, and cabinets, enabling smooth opening and closing movements. The hinge pin is inserted through the hinge's knuckles, which are the parts that connect the two objects. Hinge pins can be made from various materials, including metal and plastic, depending on the application. Proper installation and maintenance of the hinge pin are essential for ensuring durability and functionality, as a worn or damaged pin can lead to misalignment or difficulty in movement.