Abstract: A locknut which is durable and adapted to be used repeatedly is disclosed. The locknut has a body with a collar integrally extending from one end thereof for receiving a check washer. The check washer defines a polygonal hole therein. A periphery defining the polygonal hole is composed of a plurality of long edges and short beveled edges each arranged between two adjacent long edges. A length of each long edge is slightly smaller than an internal diameter of the body. By this arrangement, the extrusive portion of the long edges resulted from the thread of a bolt can be dispersed toward the short beveled edges to avoid a fracture of the check washer, thereby to maintain an effective elastic comeback of the check washer.