On August 19, 2005, about 1900 central daylight time, a Piper PA-12, N425AH, piloted by a certified flight instructor, sustained substantial damage on impact with terrain when the right main landing gear broke during a landing on runway 20 at the Boscobel Airport, near Boscobel, Wisconsin. The instructional flight was operating under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The pilot reported that he and his student were uninjured. The local flight was originating at the time of the accident. The flight instructor's accident report stated: I was giving dual instruction to a private pilot for the purpose of a tailwheel endorsement. After landing on the hard surface of runway 20, the airplane started a mild left turn towards the grass on the side of the runway. A bolt had broken on the right main gear attach bracket. The right gear folded under the airplane at about 15 mph. The gear broke and pushed the plane up in the air about 5 feet and then fell. The prop stuck in the ground. The wing bent outboard. No injuries.