IAG Fire-Lock 2.5L Head Gaskets (1 Pair with Fire-Lock Rings) For 14mm Head Studs Only- Note Machine Work with IAG is REQUIRED. After 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 compression seal once the heads are installed and torqued into place. IAG fire rings are manufactured to a very strict tolerance from a proprietary alloy and are then put through a heat treatment process. The gaskets are manufactured from an asbestos-free composite raw material and feature a silicone based beading applied to critical areas to improve sealing around all water and oil passages. The combination of the alloy compression shims and gaskets assure maximum sealing for a Subaru EJ25 turbocharged engine. Features: Composite Material, IAG-Spec Alloy Ring, Specifically designed for 14mm Head Studs, Silicone Beading, 100mm Bore, .051" Thickness, Intended for High Horsepower, High Boost applications.