On October 9, 1993, at 1719 mountain standard time, a Stinson 108, NC409, nosed over during landing roll out at Falcon Field, Mesa, Arizona. The aircraft was owned and operated by the pilot and was on a personal cross country flight. Visual meteorological conditions prevailed at the time and no flight plan was filed for the operation. The aircraft sustained substantial damage. The certificated private pilot and his one passenger were not injured. The flight originated at Marana, Arizona, on the day of the mishap about 1500 hours and had made an enroute fuel stop at Chandler, Arizona. In his written statement, the pilot reported that just after touchdown the aircraft "immediately darted to the left." The pilot was unsuccessful in regaining directional control and the aircraft ground looped off the right side of the runway. As the aircraft entered the dirt area next to the runway pavement, the aircraft nosed over onto its back. An FAA airworthiness inspector examined the aircraft and reported that one of the three bolts which secures the left wheel halves together had backed out of its associated lock nut. The protruding bolt head contacted the brake caliper and subsequently locked the wheel. An examination of the maintenance records revealed that the wheel halves were last split about two years prior to the accident when a new tire was installed.