The L-insulator is made of .250" thick high grade phenolic and features an o-ring seated on both sides. The design of this part insulates the heat from the intake manifold from getting to the carb. This allows the carb to function to its full potential. The o-ring seated on both sides creates a superior seal between the carb an intake manifold. The kit comes with the correct length and OEM style hardware to fit your 4 bolt Linkert carb.