This is the black plastic wear surface in the 9 inch long extended size (gen6 OEM). This is the original part that came with all [gen6] MAG-8000 sharpeners.
There are sequential holes drilled into this worktable so that it can be mounted to have more table length sticking out on either the right-hand side for right-handed lawn mower blades, or out the left-side for left-handed lawn mower blades. For example if you only sharpener right-handed blades you can mount this table in your MAG-8000 to support more of the blade making it easier to hold during sharpening.
This is a replacement part for the current [gen6] MAG-8000