There are small holes at the center point of the hackle gauge and the metal stand at opposite corners. Make a post by firmly inserting the supplied pin through the magnet and into the hole in the metal stand with a rotating motion. With continued use, the pin may eventually push through the metal stand. In that case, simply reposition the magnet to the alternate hole at the opposite corner of the stand. Bend a feather around the pin and see which numbered semicircle the feather tips reach. That number is the best nominal hook size for that feather. Variations in hook types will change the feather size.