Steering Rack Question

I'm in the process of rebuilding the steering rack on my '75 GT4 ... in disassembly, the round receiver nuts that lock the spherical joints of the tie rods to the rack came off fine - no problem. In reassembly, they go back on about half way and seriously bind up. I'm reluctant to force them and possibly damage threads. Has anybody else experienced this? What was the fix? This is occurring on both ends of the rack, both nuts. Nothing has happened in between - simply off then back on a few days later. ?????????