That is a good question, a very good question!
The safest way to find out is to match up to what you take off or if possible re-use what fittings you can salvage.
I have just removed the ABS pump from my Cherokee last Saturday and when I had some new pipes made up it caused problems. I walked into the shop with the snapped, corroded old pipes and asked them to make up replacements. The guy on the counter checked the fitting at one end then walked off muttering metric to himself. When I got back home and tried to fit the pipes I found to my horror that the fittings are actually a mixture of 10mm and 3/8" unf. This was 12.30, luckily a quick phone call revealed the shop was open till 3pm so I could return and sort things out (he re-used my original fittings when I went back!).
The lesson here is that the brake fittings are 3/8" unf, unless they are 10mm
I expect your slightly older Jeep (mine is a 2000 year model) will be 3/8" but don't count on it!
