amigo hitch w/spare on door no hardware? help..

ebay arrived have my hitch for my 99 amigo while installing it requires bolts that go up into the frame they were not included with my purchase this trailer hitch came from a salvage yard in colarado. I can not install it because i do not know the tread size for the drivers side bolts.. the passenger side is easy. bolts go sideways. drivers side goes up into pre threaded hole in the uni-body . Im getting ready for the season and wanna pull my bass boat. by Memorial day weekend need help. if anyone knows this answer please chime in. ding ding ding... tow-less in NY.....