Wiseco Outboard Marine pistons include twin semi-keystone rings offering maximum ring seal with less than 1% ring blow-by. Wiseco?s semi-keystone rings are a 7° tapered compression ring, chrome faced, high temperature steel alloy with ferrox coating. All outboard marine pistons are Electra coated for superior strength, wear resistance, and greater extension of ring grooves and pin bores. The coating creates a surface nearly as hard as diamonds, eliminating micro-welding of the piston rings to the grooves and prevents galling in the pin bore. Since the domes are Electra coated, along with the rest of the piston, there is additional protection against erosion from detonation. The piston also stays cooler since the coating helps reflect heat into the combustion chamber. Limited models feature Wiseco?s ArmorGlide™ skirt coating, reducing friction and piston noise.