NaZTaYBoY

I bought a Piranha G3 EXT Pro off of ebay, and it seems I'm missing a part. The marker didn't come with an owner's manual so I don't know the name of it. I need someone to help me figure out what it's called and maybe where I can get one. It's by the hammer and like on the middle of the velocity spring. It's a big black ring of some sort, between the hammer and the thumb velocity thing. I know I sound like a newbie, and that's because I am one, but I've about ripped my hair out trying to find this part, could someone PLEASE help me!