The Edelbrock Rocker Shaft Stud Kit provides better rocker shaft retention and is highly recommended for use with the Edelbrock FE heads. These studs help to eliminate thread wear and the possibility of bottoming the rocker shaft bolts on the head. Complete heads include stainless steel 2. 09 inch intake and 1. 66 inch exhaust valves to clear the 4. 050 inch bores on 390 CC engines. The size of the base thread is 3/8-16, the size of the rocker arm nut thread is 3/8-24 and the length of the rocker arm nut thread is 0. 880. The length of the effective stud is 2. 348 and the length of the base thread is 0. 655.