The pilot of the tailwheel, experimental, amateur-built airplane reported that he had completed 11 takeoffs and landings to a full stop. During a subsequent takeoff, he saw that the left main landing gear wheel was wobbling. He returned to the turf airstrip and landed at the slowest possible speed; however, the left main landing gear wheel separated, and the airplane came to rest inverted on the runway. Examination of the wreckage by a Federal Aviation Administration inspector revealed substantial damage to the right wing and vertical stabilizer. Three lock nuts that secured the wheel were missing and not recovered. Additionally, there was no damage or stripping on the threads of the respective studs. The pilot could not see the three nuts during preflight inspection as they were concealed by a hubcap. The mechanic that completed a condition inspection about 2 months prior to the accident, stated that the three missing nuts were light locknuts, made of an alloy. The mechanic removed the hubcap during the inspection as he had to lubricate the wheel bearing. At that time, he could see that the three nuts were secure; however, since they were already set to a torque, he did not attempt to tighten them.