OK, thanks. I thought I tried a 5/16" 12-point, but I'll try again to be sure. Or, I'll just try to find a 5/16" 8-point.
I'm kind of surprised that a 5/16" isn't too small. It seemed that my 8-mm open end wrench was barely large enough when I put it on there to measure it. After I saw it was a square end, I thought it looked to be 1/4", so I thought I'd be clever and use a 1/4" drive socket inserted backwards over an allen-head socket inserted over my ratchet, but of course, Dodge outsmarted me and made the square head size to be between 1/4" and 3/8"