The SeaStar front mount pivot cylinder is for Catamaran designs. This cylinder will fit ALL engines that require HC5345 steering cylinder. The internal o-ring is designed to limit the amount of fluid bypass decreasing the amount of re-alignment. This cylinder is best used in applications that require a liquid tiebar.. Cylinder ending in "3" has been updated and fit the same applications as the prior models. Improvements over previous models include: Updated styling, a more robust barrel, new sealing systems and materials with excellent resistance to compression set, and new adjustable stainless steel O-ring fittings (ORB).