Here is what I have run into with aftermarket door handles and knobs. They are not made correctly for original shafts where the set screws are supposed to go.
The issue is the depth where the splines end. There is a recess in the shaft for the set screws to go-to prevent the handle from falling off. This recess in new handles in too deep preventing the set screws to engage it.
Another issue is that the set screw is not tapered to a point like the originals and does come with a lock screw to keep it from backing out. I don't believe that the threads are the same as originals either, preventing you from using the original screw and the lock screw.
