Compression is everything when it comes to keeping your outboard running strong, and the Mercury Marine Piston Ring Set - 39-893525A01 delivers the tight seal your engine depends on to make every stroke count. Built to handle the heat, pressure, and non-stop action of marine performance, these factory-engineered rings are made for select Mercury outboards - ensuring a precision fit straight out of the box.. Crafted from heat-treated materials that stand up to high combustion temperatures and constant exposure to water and oil, each ring is machined to exact tolerances for optimal sealing. They lock in combustion pressure, keep oil where it belongs, and help prevent blow-by that robs power and efficiency. Whether you're rebuilding after years of reliable service or replacing worn rings to restore compression, this set gives your engine the sealing power it needs to run like it should.. What stands out:. Direct OEM fit for select Mercury outboards - no guesswork or trimming. Heat-treated