I am designing a 6" female thread dia. screw in flange for a marine electronics housing (surface application, low pressure). I am looking for the best thread design (standard) for ease of assembly (~3 turns to attach), and durability. The female mating flange will be metal (Ti), and the male screw in flange will be delrin. I will be using o-rings for sealing, but would like some taper on the threads to prevent back-out. I am inclined to look at API thread standards; any help will be greatly appreciated. Thanks