Phillips Flat heads are cone shaped for use in countersunk holes and have a flat top that fits flush with the mated surface. ZAGO’s self sealing screws feature a rubber “O” ring device that creates the ultimate seal around the screws. How does it work? When torque is exerted on the screw, the “O” ring reshapes and fills in the space around the screw completely, creating a very effective seal. This seal stands up against all kinds of contaminants and chemicals, and keeps the screw strong even in the face of pressure, vibration or extreme temperature. That way, equipment, with screws never compromised, will keep functioning at optimal levels for years to come.