An employee was using a pipe threading machine to thread a 2-inch diameter gas pipe during the rebuilding of a gas meter. The pipe was in a vise mounted on the back of the crew truck. A few pieces of metal chips or shavings caused the threading machine to jam. The employee started to back the pipe up, but it jammed in that direction as well. While reaching to pull the handle back up into place to try and start again, the machine rotated about an inch and pinched his middle fingertip against the edge of the truck s back step. The employee's fingertip was partially amputated without loss of bone.