.030" thick 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. Standard 3-1/2" bore. OEM replacement reference 16770-84D 16770-84F. 84-99 B.T.(excl. Twin Cam) 88-22 XL1200 (excl. 08-12 XR1200) (NU)