lt's been many, many, moons ago, but when I was in high school my weekend job was at U-Haul repairing trailers, washing trucks, and installing hitches. I would clamp the hitch to the frame, then, using whatever sized bit I needed for the bolts, start it just enough to mark the center. Then go back and drill it out with a 1/4" bit and finally, drill it out to full size which I believe was 1/2". Some frames were tougher than others, and sometimes I was out of sharp bits; in those cases, I would put a jack under the drill and let it do the work. There was nothing special about the bits, and I don't know if the fancy bits we have today were even a thing back then. All I know is that we had the cheapest bits available. One thing to watch for is the hot little metal shards falling down into the crook of the elbow between the bicep and forearm. Either be tough or wear long sleeves. Some hitches will match up to existing holes, some hitches will have a couple of hole match up to existing and the rest need drilled out. It wasn't very often that I had to drill all of the holes.