Both pilots reported that after performing airwork they returned to the departure airport where multiple uneventful full stop landings were performed. They then departed and while on the base leg of the airport traffic pattern the right main landing gear did not fully extend. At that point the designated pilot examiner (DPE) took the controls from the pilot applicant, and during the course of 90 minutes, made multiple attempts to fully lower the right main landing gear that were ultimately unsuccessful. The DPE then elected to land with the landing gear retracted rather than with two landing gear down and one retracted. After touchdown the airplane came to rest near the runway centerline. The underside of the fuselage was substantially damaged during the landing. After raising the airplane from the runway, the right main landing gear was manually pulled out of the wheel well and during that process it was discovered that the hardware that secured the upper and lower torque links were not in position and could not be located. Since the hardware could not be found, no determination could be made as to the reason for the separation of the hardware. A review of the airplane’s maintenance records revealed that the hardware securing the right main landing gear torque links was replaced last on about 11 months before the accident. At the time of the accident, the airplane had accrued about 324 flight hours since the hardware replacement. The mechanic who performed the last 100-Hour inspection, about 6 months and 46 hours before the accident, reported that he did not notice any abnormality or defects with the torque link bolts at that time.