A simple but effective port for easy filling of a water loop. The flat design makes it unobtrusive, so it fits in with most cases and blends into the overall look without being disruptive. The included stop plug screws in almost all the way, so it closes almost flush. Therefore, you get a port with the Alphacool Apex Fillport that doesn't protrude and looks like it belongs to the case instead of being retrofitted.
black version: https://www.alphacool.com/detail/index/sArticle/29437
chrome version: https://www.alphacool.com/detail/index/sArticle/29438