In hollow rectangular solid material (RHS) construction, the hollo bolt (TM) was developed to fasten materials such as steel I-beams to this hollow but strong material. Hollo bolt fasteners are used around the world in the construction of multi-story buildings, bridges, highway overpasses and various other applications where solid metal hollows are fastened together. 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 pipes, without actually removing any of the metal. The hole is automatically sealed around its edge as it is formed. A tool called a threaded roll then draws a thread on the circumference of the hole, allowing it to accept a standard threaded bolt as a fastener. The Hollo Bolt The Hollo-Bolt assembly has 3 parts, the cone, the body and also the threaded bolt. It is pre-assembled and comes in a wide range of sizes for various clamping requir