Step One:
First, you should slide the bolt through the installation material and screw the castle nut onto the other side. Use a pencil to mark the area where you need the hole to be. After that, remove the nut and bolt and place the bolt into a vice.
Step Two:
Screw the nut back onto the bolt and align it with the mark you made earlier. This will be your drilling point Make sure you drill upright to the hole so that it comes out in between the peaks on the other side as well.
Step Three:
After you have drilled your hole, remove from the vice and place it back into your installed material. Take a pair of pliers and bend the cotter pin away from the center on each side. This will create a locking mechanism and the pin will not be able to fall out.