A standard 1/2 coarse bolt would work. If you were trying to get the head that is made for the concave hole, there are two possibilities. First is to try the parts store to see if a they have a lug bolt in your thread diameter and thread pitch. The second possibility is to use a standard bolt with a convex washer. I received that style washer with a suspension lift kit from BDS. Suspension Lift Kits | BDS Suspension | Jeep Chevy Ford Dodge Toyota
It fit the skid plate on my YJ perfectly. See if the washers are available separately Hope this is of some help.