ZAGO Mil Spec 3212/3213 Phillips Pan Head seal screws are engineered with a Silicone or Fluorosilicone O-ring under the head of the screw. Once torqued, the O-ring expands and forms an unbreakable seal, preventing contaminants, such as water, ice, dust, dirt, moisture, and saltwater, from leaking into or out of equipment and potentially damaging it or the environment. Pressure-tested to military standard 1,500 psi, ZAGO Mil Spec sealing screws meet DFARS, REACH and RoHS requirements. Made in the USA/Buy American Act compliant.