This 1 inch tall phenolic thermoset plastic spacer insulates your carburetor against manifold heat keeping it cooler and helps prevent fuel percolation (also known as vapor lock) in hot weather. This can also allow for a denser fuel mixure to help increase performance in some applications, as well as provide additional plenum volume. Open center design fits Holley 4150/4160 4-barrel carbs as well as most Carter and Edelbrock models with a squarebore design. Gaskets, studs, washers and nuts are included.