On April 20, 2002, about 1230 mountain daylight time, a tail-wheel equipped Stinson 108-2, N959D, experienced a right main gear collapse while on takeoff roll at the Helena Regional Airport, Helena, Montana. The commercial pilot and the two passengers aboard the airplane were not injured, however, the airplane sustained substantial damage. The Title 14, CFR Part 91personal flight was being operated in visual meteorological conditions, and no flight plan was filed. The pilot reported that he was departing from runway 34, and that shortly after applying power for takeoff, the airplane started to track left of runway centerline. During his attempts to correct the situation, the airplanes right main wheel assembly and right landing gear strut collapsed, resulting in substantial damage to the firewall and right aileron. Post-accident examination of the Cleveland wheel assembly (model 40-113X), and tire (McCreary size 8.00-6), installed on the accident airplane, revealed that the outboard wheel subassembly fractured in multiple locations along the bead seat ring. Multiple fractures were observed in the inboard wheel subassembly, and the brake disc had partially separated from the wheel. The Type Certificate Data Sheet (TCDS), number A-767, for the Univair (Stinson) 108-2, lists multiple approved wheel-brake assemblies for the airplane. The Cleveland 40-113X wheel assembly is not listed as one of the approved installations. A representative from Parker Hannifin Corporation, Aircraft Wheel and Brake Division (Cleveland), also reported that the accident wheel assembly was approved for use with 6.00-6 and 7.00-6 sized tires, but not with 8.00-6 sized tires. Reviews of the maintenance records for the accident airplane indicate that the wheel assembly was installed on August 1, 1991. The records also indicate that the airplane's last inspection, an annual inspection, was performed on March 7, 2002.