what is gary rossington doing here

[leojb23]

 

so in this image from a live clip of free bird where hes playing slide , theres something under the strings at the first fret, what is this and whats it for ive never seen this before. cheers leo

[ezbass]

I imagine it’s primary purpose is to raise the action for slide playing, without having to alter the bridge and thus be able to remove it quickly for normal playing. It would also alter the tuning, effectively raising it a semitone.