.050" MLS (multi Layer Steel) head gaskets; final crush .042". With cylinder base O-rings. Includes 2 cylinder head gaskets; 2 cylinder base O-rings and oil return O-rings for stock 3-3/4" bore as used on 88"/96" Twin Cam models. Replacement reference 16775-99B head gasket; 11256 O-ring and head & base kit 17047-98. MLS explained: MLS (Multi Layer Steel) is used in high performance head gasket applications. They consist of multiple layers of steel uniquely designed and riveted together; outside the gasket surface for ease of installation; and provides a high performance seal.