EE was installing tromell on #3 Mill. EE was attempting to tighten the bolts w/ a spline drive impact. EE squeezed the trigger, the impact unthreaded the nut. EE's left hand was supporting the weight by the socket. The nut unthreaded the impact dropped & EE's right pinky finger was struck between the socket & the frame of the tromell. EE sustained a fracture to tip of finger.