The Edelbrock Metering Rods are designed for use with the Edelbrock Performer Series and Thunder Series AVS carburetors only and not with any other brands. These metering rods allow you to fine-tune your carburetor for optimum performance and are used to control the air/fuel mixture. Since metering rods are available with different step combinations, it is possible to independently alter the air/fuel ratio for both cruise and power modes with a single rod change. The small area at the tip of the rod is the power step and the thicker area next to it is the cruise step with a dimension of 0. 067 x 0. 055. These rods can be changed in seconds by removing the single hold-down screw and are sold as a pair.