A lock for an implement turnbuckle includes an apertured plate attached directly to the turnbuckle. The plate receives the pin or linkage connecting structure that attaches to the threaded eyebolt of the turnbuckle. The mounting end of the plate opposite the slot is secured against a flat on the internally threaded member of the turnbuckle by a U-bolt. The plate prevents relative rotation between the eyebolt and an internally threaded member receiving the eyebolt to thereby maintain the desired turnbuckle length adjustment.