Abstract: This invention pertains to the lock cylinder of a rekeyable padlock. According to a preferred embodiment of the present invention, a rekeyable padlock is provided with a lock cylinder formed within. The lock cylinder includes a cylindrical core formed to receive a key and an outer casing formed around the core. A viewing opening is formed within the casing wall, the viewing opening allowing access to pin openings formed within the core to receive selected pins. The viewing opening is shaped such that it provides a viewing area larger than the pin openings, thereby allowing greater visibility when the pins are placed within the pin openings. The advantages of this viewing opening include greater ease in placing the pins into the pin openings and easier detection when a selected pin is the wrong length and does not sit flush within the lock cylinder core.