A small plastic square on the top of a new radiator, it can slide back and forth but doesn't seem to serve any purpose. There's one on every radiator in the house
Amazon.com: Rexka 10pcs Bumper Radiator Support Splash Shield Fender Liner Engine Grill Push Type Retainer Clips 7mm Hole for Toyota Lexus 90467-07211 4Runner Avalon Camry Land Cruiser Prius GX460 IS250 RX350 :