I found this bolt head under my car on the floor of my garage. There was also a small rust stain that must have dripped from where the head broke off. The stain was on the driver side just inboard of the left front tire. I haven't had a chance to get under the car to look around yet. The bolt head measures 19mm. Anyone know what this is? My CX-9 is a 2018 with 47K miles.