EMPLOYEE WAS CHANGING TRACK PINS ON A CAT D-11 DOZER. A PIN WAS PRESSED OUT OF THE LINK. THE RAIL HALVES WERE STUCK TOGETHER BY A SMALL LIP ON THE INSIDE BORE OF THE RAILS. EE WAS HOLDING A SMALL HYDRAUULIC RAM BETWEEN THE RAILS TO SPREAD THEM APART. WHEN THE LINKS SEPARATED EE'S THUMB WAS PINCHED BETWEEN THE TRACK & A TRACK ROLLER.