Rubber flaps for fan shrouds. Street Rods by Michael, Inc. uses these flaps so when you are moving forward they let the air flow through your radiator and the shroud. This lets the radiator cool better at highway speed. Then when you are in traffic and the electric fan comes on the flaps will suck down against the shroud holes to let the fan do its job. This allows the fan be more efficient.
1/8" Drill bit for holes.