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. Our proprietary "Fire-Lock™" Head gasket system has been proven in our record-setting race cars to be the strongest Subaru head gasket system ever produced. To achieve these results, our engineers separated the combustion chamber sealing from the fluid sealing aspects of the head gaskets. These gaskets have been tested in excess of 1000 horsepower. 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. The gaskets are manufactured from an asbestos-free composite raw material and feature 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 assures 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.