Use the washer measurement to choose which size spacer you need. 3D print the spacer or order it printed online. The red arrows point to a lip on the spacer that aligns to the outer edge of the track. This keeps it from spinning once installed.

The included (.stl) files have elongated (rounded cylindrical) holes on each end to allow for left or right tracks and different hole spacing.

See the attached files at the bottom of the page and download the size you need.