Brake pipe thread sizes

Does anyone know the thread type/ size for a 93? I tried to install new hard lines at the w/e and ended up mushing every tread I touched. The strange thing was, that I got a professional mechanic to make up the new lines, and we triple-crosschecked all the old and new threads against the new proportioning valve that I'm installing at the same time. Sooo, in theory, I should have had a straight swap in.

OK, it's been suggested that over time the threads just lose strength and collapse on themselves (which is what I assumed happened) if asked to do anything, but have I overlooked the possibility of non-matching thread types? The stealership's mechanics seemed to think that they were "standard", but are they Whitworth thread, as opposed to UNC (which I consider standard), or are they something else entirely?

Somewhere in the mid-90's, the XJ went from using all SAE "double cone" type flare fittings on the brake lines to using some (not all) ISO "bubble" type flare fittings.

When that happened, the threads on the bubble flares went to metric thread. I suspect you are trying to use a metric flare nut on an SAE hole, or vice versa, and that's why the threads are getting bunged up. Look at the actual flare itself, and that will be a clue to the thread type.