1 SET Black Carb spacers 2" Tall Open Phenolic Carburetor Spacer Compatible w... About this item Compatible Information:Compatible with 4 barrel carbs with a square bore base like the Holley 4150/4160, Barry Grant, Carter and Edelbrock,that are used on many Small/Big Block Chevy, Ford and Chrysler Mopar engines. Thickness : 2" Phenolic materia l:Phenolic material is a type of plastic resin which has excellent insulating properties,Made of phenolic resin and engineered to reduce heat transfer from the intake manifold to the carburetor that provides a denser air/fuel mixutre for increased power and efficiency. Package list :Package Includes mounting hardware and gaskets. Open Design Spacers: The open design spacers increase plenum volume for improved high rpm power, while 4-hole designs increase mixture velocity for improved low-speed and mid-range torque.