The Carburetor Idle Mixture Screws will fit directly into the base plate of your carburetor. They will allow adjustment to the idle circuit inside of the carburetor base plate. Once the idle mixture is set, the speed of the idle is increased. If the idle mixture screw does little or nothing, the carburetor is probably clogged with deposits of dried gasoline and sludge and it needs cleaning and rebuilding. The screw is made of steel and has a gold iridite finish. It weighs approximately 0. 03 pounds and includes new springs for a simple installation. They fit best to Performer Series and Thunder Series AVS carburetors. The kit includes 2 idle mixture screws and springs for the square-bore carburetors.