Abstract: A hook is capable of hooking a chain at a desired length. The hook comprises a hook body, and a buckle above the hook body. The buckle has a U shape opening. Width of the shape opening is confined by the size of a chain to be hung. The buckle, has a penetrating groove which penetrates two inner sides of the buckle and one outer side of the buckle. A spring and a movable shaft pass through the penetrating groove. The movable shaft is positioned by a pin so that the spring is compressed by the movable shaft and the movable shaft will not drop out of the buckle. A notch is formed at a predetermined portion of the movable shaft. A semi-round groove is formed at a coupling portion of the buckle and the notch, and the semi-round groove is positioned across the two inner sides of the buckle.