Fricken Hamster

Does anyone know the size of the bolt that connects the seatbelt bucket to the seat? I'm trying to attach it to my sparco seat bases. A m10 1.25 pitch nut fits the threads, but it is super loose and wiggles around until its tight. Its barely smaller than a normal M10.

I guess I could find a normal m10 bolt and stack a few washers to make a spacer for the bucket if I can't find a perfect fit, or use nyloc and threadlocker and hope it stays.