THE INJURED STATED HE WAS HELPING DRILL OPERATOR BREAK TWO DRILL STEMS APART. THE STEEL CLAMP/BREAKOUT WRENCH WASN'T HOLDING THE DRILL STEM FIRMLY. MECHANIC PLACED 2"" X 4"" X 16"" BOARD BETWEEN THE DRILL STEM AND BREAKOUT WRENCH TO INCREASE GRIP ON DRILL STEM. HE MOTIONED THE DRILL OPERATOR TO TIBHTEN THE DIE GRIP ONTO DRILL STEM. WHEN THE WRENCH MOVED QUICKLY IT CAUGHT HIS RT THUMB.