I am quite handy but I've never bothered to try my own car maintenance. But I want to start with oil changes so I know how. After crawling under my 2008 Subaru Impreza and finding the oil drain plug I noticed that it wasn't simply a normal hex head bolt but rather a "reverse" or "concave" head, I've never seen this before. How am I supposed to remove it, I don't even know what to search for to buy. I tried to find a close photo of something similar as shown below.