Phillips countersunk head screw

     Made of alloy steel, these low-profile Screws are nearly twice as strong as their stainless steel counterparts. With half the height of a standard socket head, these low-profile screws fit in tight spaces, but are weaker than standard socket heads. Length is measured from under the head.

     Black-oxide steel screws are mildly corrosion resistant in dry environments. Zinc-plated steel screws have a zinc outer layer that protects the steel under it from rust, extending the life of the screw.

    Class 8.8 steel screws are medium-strength, so they`re strong enough for use with most machinery and equipment. Class 10.9 steel screws are high-strength-they are at least 25% stronger than Class 8.8. Use them for high-stress applications such as valves, pumps, and automotive suspensions.

     Coarse threads are the industry standard; choose these screws if you don`t know the pitch or threads per inch. Fine threads are closely spaced to prevent loosening from vibration. They are not compatible with coarse threads.