On July 4, 2018, about 0930 eastern daylight time, a Piper PA-28-180, N8314W, was substantially damaged while landing at Thomaston-Upson County Airport (OPN), Thomaston, Georgia. The student pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated from Griffin-Spalding County Airport (6A2), Griffin, Georgia, around 0830. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.According to the pilot, he performed a preflight inspection of the airplane with no anomalies noted. After departure, he completed one full stop landing at 6A2, before departing for OPN. While on final approach to runway 12, he configured the airplane for landing and lined up with the centerline of the runway. The main landing gear touched down on the runway numbers, and when the nose landing gear contacted the runway, the airplane veered to the left. The pilot attempted to counteract the turn by applying rudder, however, the airplane continued to the left side of the runway. The right-wing tip touched the pavement, the propeller struck the runway, and the nose landing gear wheel separated as the airplane continued off the runway. The airplane came to rest about 75 ft off the left side of runway in a grassy area. Examination of the airplane by a Federal Aviation Administration (FAA) inspector after the accident revealed that an engine mount was substantially damaged, and the nose landing gear and right wing incurred minor damage during the accident sequence. The rod that attached the nose wheel to the nose landing gear assembly remained in the nose wheel fork and was bent. However, a nut that secured the nose wheel onto the rod of the nose wheel fork was not located. The runway was searched, and it was still not located. According to FAA airworthiness records, the airplane was manufactured in 1965 and was purchased by the pilot in November 2017. It was powered by a Lycoming O-360-A3A, 180-horsepower engine equipped with a Sensenich fixed pitch propeller. According to airplane maintenance logbooks, the most recent annual inspection was completed on November 10, 2017, at a total time of 2,599.2 hours. The landing gear wheel attachment part was sent to the NTSB Materials Laboratory for examination. The examination revealed that the part was a 3/8-inch rod threaded on both ends. One end had a nut attached and the other end exhibited bare threads. Further review of the threads revealed that they had been deformed in a manner consistent with the nut having been pulled off the threads. According to the FAA Inspector, the nose wheel had not been removed since the annual inspection and the airplane had over 250 landings since the last maintenance on the nose gear tire. According to the pilot, the nut that secures the nose wheel to the rod and fork assembly, that was not located, cannot be seen during a preflight inspection since it was covered by a wheel fairing.