it's a butt splice but a little more high tech. We use them in aviation for various applications. It's a metal sleeve that's crimped with a special crimping tool made just for that splice that crimps 360' of the barrel not just a pinch, and then there's a shrinkable sleeve that's heated like shrink wrap but it seals better and is hard when done. Regular shrink wrap stays soft when done. I did all mine in this fashion and have had no problems.
