.030″ MLS (Multi Layer Steel). Stock 3″ bore. MLS (Multi Layer Steel) consists of a top and bottom layer of stainless springsteel which is covered by high temperature rubber on both sides. The inner ring is also stainless steel. These 3 layer gaskets are rivited together, outside the gasket surface, for ease of installation. MLS head gaskets eliminate the use of dowel pin o-rings.