Water flow restrictor plates. Mounts under water neck on intake manifold instead of a thermostat. Supplied with 3 different sized plates (5/8", 3/4", and 1" opening) to restrict water flow for improved heat dissipation and cooling. Allows you to control water flow (without a thermostat) for optimum efficiency. Cars running a lot of rear gear can actually pump the water too fast, not allowing sufficient time in the radiator to cool down. Fits all GM V-8s, GM V-6s, and small block fords. Set of three.