On August 26, 1997, at 2000 central daylight time, a Fingerhut Revolution Mini 500 homebuilt helicopter, N570F, was substantially damaged during a forced landing near Huffman, Texas. The student pilot, sole occupant of the helicopter, was not injured. The helicopter was owned and operated by the pilot under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the local flight for which a flight plan was not filed. The instructional flight originated from a helipad at the pilot's home in Huffman, Texas at 1945. According to the pilot, he experienced a disconnect of the collective control system which resulted in the main rotor blades going to flat pitch while in cruise flight at 800 feet MSL. The pilot added that he elected to execute a running landing to a cultivated field rather that try to land in a confined helipad. During the landing flare the helicopter yawed to the left as the pilot applied collective to cushion the landing prior to touching down. The pilot added that the helicopter was not properly aligned during touch down and the helicopter rolled over on its side. The FAA inspector confirmed that the 1997 model helicopter sustained structural damage. He added that the student pilot was properly endorsed for solo flight and had accumulated a total of 50 hours of flight in helicopters, of which 28 were in the same make and model. According to the aircraft maintenance records, the helicopter had accumulated a total of 28 hours since it was assembled by the pilot from a kit. Flight control continuity was confirmed by the FAA inspector to the cyclic and anti-torque systems of the helicopter. Examination of the helicopter by the FAA inspector revealed that a disconnect of the collective flight control system between the collective riser block (P/N 0153), and the rod end (P/N 0600) for the collective control rod (P/N 0002). With the aid of 10 power magnification, the inspector examined the threaded areas of the collective riser block and the rod end. The threads on the aluminum collective riser block were found to be displaced or pulled out. See enclosed drawing showing the 0.314 inch penetration on the threaded surface of the riser block and the first 0.388 inch engagement on the rod end. The FAA inspector also noted that the control rods provided by the helicopter manufacturer were not provided with a "witness hole" so either the installer or an inspector could verify the amount of rod end penetration into the threaded control tube. Furthermore, the assembly instructions provided by the manufacturer did not stipulate the minimum amount of thread engagement required in any of the rod ends in any of the flight control tubes in the helicopter, nor did it warn the potential builder of the criticality of proper thread engagement and security. To assist with the investigation, the FAA inspector inspected a like helicopter to establish a comparison on the installation of the flight control systems. The comparison between the two installations revealed that a pronounced difference existed in the length of exposed threaded areas between the rod ends and the control rods. The owner/builder of the helicopter provided the FAA inspector with the plans and instructions provided to him by the kit manufacturer during the assembly of the helicopter.