The XL Freak Back is part a of a two piece paintball barrel. This uses the most current XL inserts that are longer than the original freak system inserts. These backs come in different thread for several paintball markers, but this one has the Cocker threads, which are common on many paintball guns. You will need to pair this with a front (tip) and sizing insert. This back is most commonly purchased when you already have a Freak Kit, but want to use with a gun that has cocker barrel threads.