Hello. All of the bolts on your car are supposed to be course thread. The earlier cars had some fine thread bolts, though. On my car, a 64 1/2, the bolts holding the coil spring cover are 5/16-24, as is all of the shock and shock tower cap hardware, along with the bolts holding the horns onto the strut rod brackets. The 65/66 cars had mostly course thread stuff, but, the shock mounting hardware and shock tower cap stuff is supposed to be fine thread. A whole bunch of Ford stuff that wasn't Mustang from the 64 model year and earlier had fine thread bolts.I have never come across any fine thread 5/16" bolts on my car; all are coarse thread.