You will need eight 6mm nuts with washers to go on the eight threaded studs on the rails that go through the seam on the bottom of the body.
You will need four bolts and four j-nuts (like these). I don't know the metric size that Jeep lists but I used 5/16". The j-nuts clip into the bottom of the body and the bolts thread through the mounting tabs on the rails into the j-nuts.
If you have a 4 door adjust your quantity accordingly.
I got all my hardware at Lowes. The j-nuts will be in the drawer for specialty hardware or automotive hardware, don't remember which one.