Mount a ¼" thread to the back of your Ergotron LX VESA mounting plate.
This gets attached to the back of the VESA 100x100 mount by the thumbscrews included with the LX.
The tolerances should be tight enough to fit without wiggling.
Requires a Ruthex RX-1/4"x12.7 insert.
I used this to mount a magic arm and my webcam.
The author marked this model as their own original creation.