The cylinder liners that are used on the AT use a three ring design. The bottom two rings are round but the top ring is square cut. This top ring sits in a square cut groove and is called a trash ring. This provides protection from crevice corrosion that could attack both the liner and the lower sleeve bore in the crankcase. The liners are also bath nitrided. Bath nitriding is a surface hardening process that provides a more wear resistant surface to the inside of the liner while making the outside more resistant to cavitation.