The Factory Fatty is reminiscent of the "works" or cone pipe once used by Factory Teams. It shares many of the same characteristics with it's craftsmanship and material quality. The Factory Fatty broadens and smoothes out the power curve while boosting gains throughout the entire power band, more low-end, more mid, and increased over-rev. No matter what type of riding you do, the Fatty has the benefits you're looking for. Features: Lighter 20 gauge steel used for the body of the pipe. 19 Gauge steel used for the header portion. Includes O-rings on most models Hand pounded seams for smooth flow transitions. O-Rings Included Fitment: Yamaha YZ250 1999-2021