Allstar Performance ALL30133 Radiator Cap Higher Cooling System Pressure Raises The Boiling Point Of Coolant To Reduce The Risk Of Overheating Standard Size Caps Fit 2-1/8" O.D. X 3/4" Deep Necks Unless Otherwise Noted. Recovery System Caps Allow Coolant To Exit The Cooling System Into An Overflow Or Recovery Bottle As Coolant Heats And Expands