3 core connector from the lights to the controller. By not soldering the lights directly to the controller you can swap the lights, swap the controllers, repurpose the controllers if you need to, attach a controller with test firmware without having to reflash the chip, remove the controller for repair or upgrades without having to take your lights down or even have them on your workbench. Is that enough reasons. LOL Buy extra because you will be surprised where and how you decide to use them. I have only used 4 core for my dumbstrings. Any SSC with the rj5 jack are tucked under my eaves or my porch roof. Any that are exposed, I just put a long piece of coax on them and run it straight into my battery box to the hub so no rj45 connections are out in the open. But if I needed to I would use the 4 core waterproff connectors.