A slightly elastic plastic “hood” that is slid over the multi clip (this connects the leader to the swivel lead) and serves as an end stop / buffer for the Big Eye Swivel or Heli-Chod Speed Swivel.
These swivels are brought to the direction of the plumb during the fight. This extra strong Heli-Chod Hood can withstand the pressure of a tough fight. This is because this buffer is quite massive with a narrow passage, but has a short space where the multi clip and swivel of the lead fit nicely.