I wanted a gaff for my kayak when going offshore but did not want to go the traditional gaff route so I decided to make my own version of a hawaiian / kage spear gaff. The 3d printed insert goes into a 1 inch tube which will support the stainless steel all thread that will become the spear. The included video shows how it all goes together using a 5/16" rod.
The file for the rod / nut insert is available in four different sizes. Select for the size rod that you are going to use: 5/16", 3/8", 7/16" or 1/2" diameter rods.