Rear disc brakes

Yeah its seems crazy. To make sure I wasn't crazy I went and double checked just now lol. This is the drag kit with an aluminum hat that I had to drill for my larger studs.

I believe it is this kit Wilwood Disc Brakes if you click on the rotor hat it will take you to another page with the face thickness and other dimensions. 0.50 inches.
I guess it's because the hat is aluminum.