EMPLOYEE WAS ASSISTING REMOVING BOOM FROM ST8B AT THE BUICK UNDERGROUND SHOP AREA. EMPLOYEE HAD REMOVED THE ""BOOM TO FRAME"" PIN AND WAS TOSSING THE PIN ON TO THE NED OF THE UNDERGROUND SHOP TRUCK. A CLOTH HAND TOWELL WRAPPED AROUND EE'S RIGHT HAND BECAME ENTANGLED WITH THE PIN. THE PIN FELL ON THE EE'S RIGHT HAND, MASHING IT AGAINST THE BED OF THE TRUCK.