These ones work! It took a lot of not knowing what I was looking for and then ordering the wrong stuff to get here. I also learned that Vector is a brand, not a type of rail.
In any case, Vector brand rails and Schroff brand threaded inserts work beautifully together, as long as you don't mind using smaller M2.5 screws. Both the rails and inserts are 84HP long (42.672cm or 16.8").
And if you're bonkers and want to use sliding nuts:
- Vector Electronics NT4-7PA M2.5 Sliding Nuts x 25