The BRIGGS & STRATTON 590521 Engine Piston Assembly helps maintain proper compression and smooth movement inside the engine cylinder. The piston moves up and down within the cylinder to compress the fuel-and-air mixture and transfer combustion force through the connecting rod. This assembly is identified as a standard piston assembly and is used with related piston rings and pin compo... https://www.wholetoolbox.com/briggs-stratton-590521-engine-piston-assembly/590521.html