A hook rule is useful for woodworking, but instead of spending the extra money to buy one, I make mine with shop supplies instead. I use a couple of rare-earth magnets to turn conventional rules into hook rules. On thicker steel rules, just snap a large magnet right to the end, as shown in the photo here. It forms a perfect 90° “hook” to align the end of the rule precisely with the end of a workpiece. For thinner rules, place the magnet on the rule’s face so a portion of it extends past the rule’s end. Then affix a smaller magnet or even a machine nut under the larger one in the overhang area. Push the smaller magnet against the rule’s end to form the hook.
– Serge Duclos