i once replaced a tie rod, and to keep the toe-in the same, i counted the threads on the old one, and set the new one to the same number of threads. what i didn't know is that the new part had a different thread pitch, so the wheels were toed-in about an inch. i went through 2 pairs of front tires in about a month. when i saw the knife-edging on the tread of the tire i figured out what was wrong. it took a long time of adjusting to get it right (measure, twist the coupler, measure again, etc...). i came up with an idea for a pair of laser pointers (actually laser sights for a pistol would be better because you can adjust the X/Y deflection on them ) mounted on magnetic mounts theat would seat just inside the lip of a rim. if you know the distance between the rims, , the distance the mounting points are from a facing wall, and the required toe-in (on many cars it's zero, which makes things much simpler), you can figure out where the lasers should land on the wall, put a couple of markers on the wall, and adjust until the lasers are on the marks.
the reason you may need to adjust the X/Y deflection of the beam is so that you can make sure the beam is parallel to the axis of the magnetic mount.