Material and Color: Material: Made of High Quality Aluminum. Color: Black Specification: 1.100% Quality Assurance Tested, More Responsive, Cheaper, Easier to Install.2. Flare caps block the fuel hose line, prevent dirt and debris from entering the adapters.3. Anodized for excellent appearance, anti-corrosion durability, long lasting and strength.4. Designed to seal tightly with any manufacturer of adapter fittings.5. Completely reusable, simply disassemble and place on another hose.6. Precision machined to exact tolerances for trouble-free performance.7. Maximum pressure: 4000psi (275bar).8. Operating temperature range: -65 deg; f to + 252 deg; f (-53 deg; to +122 deg;).About locking nut: A thread is a special type of fitting used to connect flexible hoses and rigid metal pipes that carry fluid. It became popular for use in professional racing due to its ability to easily adapt new lines. From there, it spread to the automotive performance aftermarket due to its adaptability, upgradeability, and durability. Installation Steps: The hexagonal shape is easy to install. Screw in by hand and tighten with a wrench. An adjustable wrench is recommended. Package includes: 1pcs x Flare Cap Pipe Fittings. (100% Brand New Never Used or Installed)