Cast Piston for 2 StrokeBecause of a cast piston?s ability to contain higher silicon content compared to forged pistons, and because twostrokes have lower cylinder pressures when compared to four-strokes, cast pistons are ideal for two-stroke engines. Vertex pistons are gravity cast from an aluminum alloy with18% silicon content. Silicon is important because:- It decreases thermal expansion, which changes the geometry after the piston reaches operating temperature. With low thermal expansion characteristics, Vertex pistons can be run at tighter tolerances compared with forged pistons. This creates better power and performance, also making them less susceptible to rattling or breaking.- Silicon gives the pistons better wear characteristics and prolongs piston life by decreasing wear on the piston skirt.Flat top Twin RingRing part number 55910005400