You will need:
An end cap, a 6" or 3" nipple, a 3/8in driver, 2 3/8in nuts
1. Drill a (3/8) or (5/16) inch hole in the head of the cap.
2. Screw one of the nuts all the way onto the threading of the driver. Use locktite or JB Weld to stop the driver from loosening.
3. Slide the driver through the top of the cap as shown in the picture.
4. Secure the driver in the cap by screwing the other nut under the cap as tight as possible. Also use JB weld or locktite to stop it from loosening.
5. Screw the cap onto the nipple.
I used a 6inch nipple. I cut it in half so that I could make 2 harpoon heads. Don't forget to drill 3 holes in the nipples so you can put 3 screws in them to attach it to the wooden dowel.