EMPLOYEE WAS POSITIONING A BORE HOLE REAMER BIT. A CHAIN WAS WRAPPED IN A CRADDLE FASHION AROUND THE STEM. THE EE WAS WALKING UP TO THE REAMER & SLIPPED, HE REACHED OUT TO STOP HIS FALL WITH HIS LEFT HAND. THE EE'S LEFT THUMB WENT BETWEEN THE CHAIN & THE CHAIN CAME TOGETHER CAUSING A FRACTURE & LACERATION TO HIS LEFT THUMB.