Charly,
took a scrap of aluminum 1/8" x 3/4" x 8" long, drilled a 3/16" hole in it, countersunk it slightly, sawed off a 3/16" length of (old, cheap, therefore soft) hex wrench. Then I used a vise to push the newly cut (therefore sharp) hex right through the 3/16" hole, it sticks real good...