EMPLOYEE WAS MANUALLY PULLING CONVEYER BELT OVER THE DRIVE PULLEY OF A CONVEYER USING THE V-BELTS ON THE DRIVE ASSEMBLY TO TURN THE HEAD PULLEY WHEN HIS LEFT THUMB BECAME CAUGHT BETWEEN TWO OF THE V-BELTS. THE UNIT WAS LOCKED OUT AND EMPLOYEE WAS WEARING GLOVES. EMPLOYEE SOUGHT MEDICAL ATTENTION AND WAS DIAGNOSED WITH A BRUISED THUMB,AND THUMB WAS PUT IN A SPLINT.