Allows you to control the rate of heat absorption from the engine block and heat dissipation from the radiator in Race Only Applications. Used by professional engine builders to obtain optimal temperature control and maximum power. Kit contains 3 anodized discs with an I.D. of 5/8'', 3/4'' and 1''. Color coded for easy identification. Fits most AMC, Ford & GM V6, V8 engines with a 2-1/8'' O.D. thermostat.