This is the hard reinforced plastic piece that wedges between the beer tower font and the shank.
If you are wanting to mix up your Kegerator / Draught System with a bit of black flair, this would be a great place to start if you already have Stainless Steel Shanks and don't want to spend money on an entire shank again.
It is important to note to be gentle with these black parts as scratches will show up more clearly compared to the Stainless Steel look versions.
