I't doesn't; the thread is titled "Magic Marker/Notebook Mod" and it's the notebook part (though the link takes you to a discussion about the magic marker part) that the black sled solves. IIRC the Notebook mod was cutting a thin rectangular frame from a black notebook cover that was either glued to the lips of the sled or press fitted into the cars opening in front of the sled. It'd allow the empeg to slide through, but cover up the lips of the sled.

/Michael