Dismanlting HTG Supply Lights

I have a 150W HPS Im taking apart (everything will be put back s it came) So I can have the ballast outside my cabinet. I got the wire nuts and everything off fine but the black thing thats around the wire going into the socket wont come off. Iv tried everything I can think of. Looks like its just one of those you squeeze and pull. After plumber pliers and robo grips didnt work though im a little lost. Anyone done this or know of anywhere I could look?

Nevermind the second I posted that I got it. For the record pinch it on the outside and wiggle.

I own two of the 150 watt HPS from sunlight supply co. The bulbs get way hotter than the ballasts any day. Your time would be better spent figuring out how to cool the fixture as a whole. I am fabbing some attachments for mine right now

I got that figured out already but every little bit helps right?