MLS (Multi Layer Steel). Front & rear gasket for one engine. 3-7/8" (3.875") fits 88" to 95"(1550cc) big bore conversions and is standard size for 103" OEM H-D engines. Will not fit 103" Twin Cooled models. Stock Twin Cam gasket is approx. .043" thick. MLS (Multi Layer Steel) explained: MLS consists of a top and bottom layer of embossed stainless steel with both side coated with 250°C high temperature polymer rubber layer. The inner ring(s) are also stainless steel. The gasket layers are rivited together; outside the gasket surface; for ease of installation. The outer layers are embossed and both sides coated with a 250°C resitant polymer rubber layer. MLS head gaskets eliminate the use of dowel pin o-rings; when in use.