Vertex 2-Stroke Piston Kit As the OE supplier of two-stroke pistons to KTM, Vertex pistons has an outstanding reputation for quality and performance. Each gravity cast piston is created with only premium aluminum alloys utilizing an 12-21% silicon content. The silicon content in Vertex pistons is crucial to the quality of the piston. Silicon is critical in decreasing thermal expansion which, when an engine reaches normal operating temperatures, can change the geometry of the piston. Controlling this expansion means that a Vertex piston can be run at tighter tolerances for more power, less noise and a longer lifespan of the piston. Plus, the silicon content decreases wear on the piston skirt which also aids in the life of the piston. In addition to the silicon, each Vertex piston utilizes a unique Molybdenum Disulphide (MOS2) coating which aids in the break-in process and reduces overall wear.