These are the mounting points:
Tow wiring harness adapter in yellow circle
Also, regarding the supplied washers. It is not even mentioned in the instructions for installing the hitch, as the manufacturer seems to write these instructions with an experienced installer in mind, but these washers have a "tooth" in them though they don't look like the usual toothed washer. The toothed side of the washer faces up to the trailer hitch when installed.
In case I didn't mention it, the new bolts have a 17mm head and have an yellow orange coating. It doesn't appear to be galvanized zinc or a phosphate type coating. I don't know what the coating is.