You drill a hole slightly smaller than the OD of the insert, for instance a ¼-20 Ultrasert II is .375"OD, drill a .359" hole. The table below gives recommended dimensions but I have often just ignored the taper and drill somewhere in between the larger and smaller dimensions. Line the tip of the insert up with the hole and slowly push it into the hole with a hot soldering iron while the plastic melts around it. I should qualify my experience by saying I have never used these around salt water. They are "brass" but I don't know what kind of brass.