This is an OEM Graco mixing chamber. This chamber has a round pattern, with .42 orifices. It has a 11 inch spray pattern, when you are 2 feet from your target. The output of this chamber is 9lbs/min. This chamber is the most popular chamber out there. It is the standard chamber for Graco. When you first bought your gun, this is the chamber it comes with. If you are not sure which chamber to use, pick this one. It is a great starting point for sprayers. Recommended for machines of all sizes!