Tap bolts are similar to hex bolts except they are fully threaded no matter what their length. They are designed to be used in drilled and tapped holes. They are used in applications where a stud with a nut on each end would be impractical. Used in low strength applications. Plain finish, or bare metal, may or may not have a coating of light oil to resist corrosion. Grade 5 is the most common grade used in manufacturing assembly.