Phenolic Plastic Carburettor Spacer, Open Center, 1/2" Spacer RPCR9139Phenolic Plastic Carburettor Spacer, Open Center, 1 2" SpacerFits Holley AFB Four Barrel Carburettors, Gasket & 2" Stud Kit Included RPCR9139 CR9139 Made out of phenolic resin and engineered to reduce heat transfer from the intake manifold to the carburetor that provides a denser air fuel mixture for increased power and efficiency. Includes mounting hardware and gaskets for a no hassle installation. Specifications: 1 2" Thickness Fits Holley 4150 4160