EMPLOYEE WAS TRANSFERRING STEEL CHANNEL BARS FROM THE FORKS OF S FORKLIFT TO A STORAGE RACK. EMPLOYEE'S THUMB WAS PINCHED BETWEEN PIECE OF CHANNEL BAR AND HIGHER RACK LEVEL WHEN UNEVEN WEIGHT DISTRIBUTION CAUSED METAL BAR TO RISE UP UNEXPECTEDLY. VICTIM PULLED BAR DOWN AND REMOVED THUMB.HE HAD NO BROKEN BONES. RETURNED TO WORK LIGHT DUTY.