This solid aluminum spacer can be added between the toggle clamp and the vertical beam on a standard mount, to push the clamping point a bit further under the desk. This is sometimes needed when desks have chamfers on the underside, or a thin lip on a desk that keeps the clamp from fully seating.
This comes with the spacer itself, and two #10-32 x 1-1/8 screws for securing it to the vertical beam on your mount. You will need to remove your toggle clamp to install the spacer.
If your desk accepts the standard mount without issue, there is no additional benefit to adding a spacer.
Note these Clamp Spacers are sizes for 10 Series Extrusion, which is used on Foxx Mount Desk Mounts. Their dimensions are 2" x 3.75" x 0.5". The mounting holes are spaced 1" apart, and are located 1.375" from the top. They have a brushed aluminum finish.