The mounting hardware for the four top holes is not supplied. The end user decides what style of mounting hardware will match the existing bolts, Allen heads, and so on. If using standard nuts and bolts, simply drop them into place and tighten. We opted to use stainless steel carriage bolts, which will require enlarging the mounting holes a bit more or filing the corners square for the carriage bolts to sit flush. The brackets come with square mounting holes just for carriage bolt use, too, which is a bonus.