Start with 2.0 mm rod, a coathanger will work, at least a U.S. coathanger, also welding rod. It is then bent into a U shape, 20 mm across at the bottom of the U, with the sides of the U about 2.5 to 3 inches long. The two ends of the U are then filed to a 70 degree angle inward, i.e. so that the points at the end of the U are on the outside edge. The 70 degree number seems to vary by source but not all that critical - anything close should work.