An employee was setting up tire force testing machines and changing out rims to fit the size of the tire being tested. He was mounting the bottom portion of a rim. During the mounting, the cylinder is lifted up to ensure the machine lines up properly. The rim he was mounting was off center. When he lowered the cylinder, the rim fell on his index and middle fingers. His index finger was fractured and his middle finger sustained a deep laceration between the hand and first knuckle. His finger had to be surgically amputated.