How Does a Hollo Bolt Work?

In construction with rectangular hollow solid (RHS) materials, the hollo bolt (TM) was developed to hold materials such as steel I-beams to this hollow but strong material. Developed in Britain, hollo bolt fasteners are used around the world in building multi-story buildings, bridges, road overpasses and various other applications where metal hollow solids are fastened together. Learn more about how the hollo bolt works below.

Flow Drilling

Flow drilling is the process of making a hole through hollow structural materials such as rectangular steel tubing without actually removing any of the metal. The hole is automatically sealed around its edge as it is created. A tool called a roll threader then draws a thread into the circumference of the hole, enabling 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 the threaded bolt. It is pre-assembled and comes in a wide range of sizes for various fastening requirements. The Hollo Bolt is made of mild steel, with a zinc plating to prevent corrosion. Custom-ordered Hollo Bolts can be made with high-grade stainless steel. The Hollo Bolt can also be made with a socket or button head, or a countersunk set screw head. Hollo Bolts are made in a range of strengths to provide greater structural integrity than other types of fasteners.

Hollo Bolt Sizes

Hollo Bolts are produced in sizes from 4 1/2 cm (1 3/4 inches) to 8 cm (3 1/4 inches) in length.

Advantages of Hollo Bolts

Due to the consistency of Hollo Bolts, a standard size can be chosen and used throughout the construction project, saving time and inventory costs. Hollo Bolt fasteners also minimize the number of welds that must be used to join metal to metal, reducing costs and increasing worker safety.

Inserting the Hollo Bolt

The Hollo Bolt is inserted into the flowdrilled holes in both the structural material and the item to be fastened, up to the collar on the bolt. The hexagon head of the bolt protrudes beyond the collar. Hollo Bolts may be inserted at any angle to the material from 30 to 90 degrees.

Tightening the Hollo Bolt

The Hollo Bolt is tightened by placing an open-ended wrench around the collar to keep it steady, and attaching a torque wrench of the proper size to the hexagonal head to tighten it. A powered wrench that can perform both functions at once is being developed. Upon applying torque to the hexagonal head, the flanges on the body of the Hollo Bolt spread open, anchoring the fastener deeply into the structural hollow solid material.

Sealing the Hollo Bolt

Various sealers have been developed for the Hollo Bolt to reduce water penetration. Information about these is available from the manufacturer, Lindapter.

How Many Hollo Bolts to Use

At least 4 Hollo Bolts need to be used to fasten a plate to a structural hollow solid. Usually 8 Hollo Bolts are used, in a format of 2 columns, depending on the plate's width. Measure carefully when putting Hollo Bolts through adjacent faces of the structural hollow solid so the bolts do not come in contact with each other.