If the nuts don't fit you could anneal them and mill them down. Soap
them up with Ivory etc. to cut down the scaling, put in a tin can about
half full of charcoal, heat to red with a propane torch, preferably
outdoors. Let them cool slowly by covering the can. If they don't file
easily, try heating hotter.

If you make your own don't run the tap all the way through. The rod
should jam in the threads before it touches the bottom of the tee slot.

This is the sort of job an old surface grinder is good for.

Jim Wilkins