Continuous hinges, also called piano hinges, provide support to run the full length of the doors, panels, or pieces being joined together. They also vary by knuckle length, pin diameter, leaf thickness, and open width. The knuckle is the tubular part of the hinge through which the pin passes, and knuckle length is the measurement of an individual section. The pin runs the length of the hinge holding the leaves together. The leaf is the flat metal portion of the hinge that extends laterally from the knuckle and revolves around the pin. Open width is the dimension from the outer edge of one leaf to the outer edge of the other when the hinge is fully open.