He was re-torquing tire of a coal hauler, using a air torque gun. He had torqued all lugs except lug at 6 o-clock. As he placed the gun on the last lug he hit the trigger with his rt hand.The gun being activated caused the gun to twist.This action caught his lt 5th finger between the gun extension and the wheel cover. He received a laceration to his lt. pinky, requiring sutures.