This Metal Breech made by GavinFuzzyCustoms increases durability of a part that takes a decent amount of stress, and also has flat sides that allow for magazine insertion or removal with the breech in the closed position. The included aluminum Barrel's inner diameter specifically fits the outer diameter of this breech, which offers smoother chambering than the original plastic ones, and a tighter fit on darts than most other hobby grade aluminum barrels (.527" ID). Though as a note, it should also work fine with our standard aluminum barrels which are .509" ID by comparison. Kits include:1x Metal Breech1x 13mm ID Aluminum Barrel2x Breech O-rings2x Breech / Plunger Head O-rings1x GFZ Sticker *This is a kit to replace the breech and barrel in a SPAMF, and as such, the SPAMF kit or blaster is not included.