Vertex piston kits inc the piston, rings, wrist pin and circlips. The pistons are heat-treated with a T-6 hardening and tempering cycle. Also, a molybdenum disulphide skirt coating is used for reducing wear and improving the break-in of each piston. Cast Piston for 2 Stroke Because of a cast pistons ability to contain higher silicon content compared to forged pistons, and because two strokes 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 with 18% 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 Ring Ring part number 55910005400