This scary looking thing is a Hellerman Tool
When I first saw this thing, I started thinking about interesting horror movies.
Here’s how it works. The rubber sleeve fits over the three pointy prongs. Squeeze the handle and the prongs spread the open creating a space for the mic and wire to slip through. Roll the sleeve off the prongs, remove the tool from the wire and then unroll the sleeve.
Threading Wire through sleeve using a Hellerman Tool Threading Wire through sleeve using a Hellerman Tool