The IAG Performance 1/2 Inch Head Stud Set is manufactured by ARP and is designed for use on high horsepower Subaru EJ25 and FA20 DIT engines. Due to the larger size of the head studs, a greater load can be placed on the fasteners and in turn it aids in preventing cylinder heads from lifting in race applications. The larger size of the head studs requires the case halves to be drilled and tapped. The cylinder heads will also require drilling to accept the larger studs.