IAG Performance Fire-Lock Ring 100mm Head Gaskets for 14mm Head Studs PAIRAfter years of research and development testing, the IAG Performance Fire Lock head gasket is the newest solution to preventing head gasket failure on high horsepower and high boost Subaru EJ25 engines. This solution is loosely derived from diesel technology where a counterbore step is machined around each cylinder bore allowing specially sized fire rings to drop into the machined area and head gasket bores. The shims are designed to create a