Athena gaskets are the ultimate seal for your LS engine! Available in 3.997″, 4.056″, 4.150″, and 4.174″ bore sizes. These Athena gaskets use a Stainless O-ring that cuts into the head to provide the strongest seal available for High boost or high compression engines. Because the O-ring cuts into the aluminum Head when you pull the head off you will have to surface it .0003 to .0005 before reinstalling the head. They feature the extra tabs for 6-bolt capabilities. If you are using them on a standard 4-bolt LS block, you can simply cut the tabs off that you will not use.