In Rectangular Hollow Solid Materials (RHS) construction, the hollo bolt (TM) was developed to attach materials such as steel I-beams to this hollow but strong material. Hollo bolt fasteners are used around the world to construct multi-story buildings, bridges, overpasses, and other applications where hollow metal solids are joined. Find out more about how the hollo bolt works below. Flow drilling Flow drilling is the process of drilling a hole through hollow structural materials, such as rectangular steel tubes, without removing any of the metal. The hole is automatically sealed around its edge because it is made. A tool called a threader winds a thread around the circumference of the hole, allowing it to accept a standard threaded stud as a fastener. The Hollo Bolt The Hollo-Bolt assembly has 3 parts, the cone, the body and therefore the threaded bolt. It is pre-assembled and comes during a wide selection of sizes for various fastening requirements. The Hollo Bolt is made of mild